GNU Autoconf NEWS - User visible changes.

* Noteworthy changes in release 2.72.90 (2026-02-03) [beta]

** Backward incompatibilities

*** AC_PROG_CC now prefers C23 if available.
  Older code may need to be updated, as C23 has removed old-style
  (K&R) function definitions and declarations, now uses type-generic
  functions for strchr and similar functions, and has new keywords
  alignas, alignof, bool, constexpr, false, nullptr, static_assert,
  thread_local, true, typeof, typeof_unqual.

*** AC_PROG_CC no longer checks __STDC__ or variable length arrays (VLAs).
  This ports better to MSVC, which does not define __STDC__ and does
  not support VLAs.  Although C99 requires VLAs, they are optional in
  C11 and later.  Programs can use AC_C_VARARRAYS and __STDC_NO_VLA__
  to use VLAs if available.

*** AC_PROG_CXX no longer attempts to switch to C++98 or C++11.
  Instead, it uses the compiler's default, which you can override
  by configuring with something like CXX='g++ -std=gnu++11'.
  This reverts to Autoconf 2.69 behavior, and also fixes a bug where
  AC_PROG_CXX rejected C++20 compilers.

** New features

*** Programs now recognize #elifdef and #elifndef.
  The autom4te, autoscan and ifnames programs now recognize the two
  preprocessor directives, which were introduced in C23 and C++23.

*** Support for the Algol 68 programming language has been added.
  The new macro AC_LANG_A68 sets variables A68 and A68FLAGS.

*** AC_PROG_AWK now also checks for busybox awk.

*** AC_USE_SYSTEM_EXTENSIONS now defines _COSMO_SOURCE for Cosmopolitan Libc.

** Notable bug fixes

*** AC_CHECK_DECL and AC_CHECK_DECLS will, on macOS, now report "no" for
  functions that are declared as existing in future macOS versions only.

*** AC_DEFINE_UNQUOTED no longer mishandles double-quotes inside $(...)
  and ${...}.

*** AC_DEFINE and similar macros no longer emit trailing whitespace.
  This pacifies the -Wtrailing-whitespace introduced in GCC 15.

*** AC_FUNC_STRNLEN now detects Android 5.0's broken strnlen.

*** AC_PROG_OBJC now finds the GNU Objective-C compiler, as packaged in
  EPEL 9, by default, without the user having to set the OBJC variable.

*** Autoconf no longer generates ${1+"$@"} in scripts, working around
  a bug in AIX 7.2 ksh93.

*** config.status now fails with a diagnostic if awk is missing,
  rather than misbehaving.

*** autoreconf handles projects using GNU Gettext and/or gtk-doc better.
  A variety of situations where autoreconf would try to run the
  'autopoint' and/or 'gtkdocize' tools when it shouldn't have,
  or *wouldn't* run them when it *should* have, have been corrected.
  See <https://savannah.gnu.org/support/index.php?111273>,
  <https://savannah.gnu.org/support/index.php?111272>,
  <https://savannah.gnu.org/support/index.php?111271>,
  <https://savannah.gnu.org/support/index.php?110503>.

*** autoconf no longer installs a file named "version.m4".
  This eliminates an annoying (but harmless) warning produced by
  Autoconf 2.72 when projects contain their own "version.m4".

* Noteworthy changes in release 2.72 (2023-12-22) [release]

** Backward incompatibilities

*** Configure scripts no longer support pre-1989 C compilers.
  Specifically, compilers that *only* implement the original “K&R”
  function definition syntax, and not the newer “prototyped” syntax,
  will not be able to parse the test programs now emitted by
  AC_CHECK_FUNC, AC_LANG_CALL, and similar macros.  AC_PROG_CC still
  accepts such compilers, but this may change in the near future.

  This change was necessary in order to support the upcoming 2024
  edition of the C standard (often referred to as “C23”), which will
  officially remove the function declaration syntax used by
  AC_CHECK_FUNC in Autoconf 2.71 and earlier.  We feel that support
  for compilers that support only C 2024 is more useful, nowadays,
  than support for compilers that don’t implement a core feature of
  C 1989.

*** Autoconf developers now need Perl 5.10 (2007) or later.
  “Autoconf developers” means specifically people hacking on Autoconf
  itself.  Autoconf *users*, i.e. authors of configure.ac files and
  add-on M4 macros, still need only Perl 5.6 (2000) or later.

  We do recommend all Autoconf users upgrade to Perl 5.10 or later if
  possible, as this version significantly improves Perl’s ability to
  handle files with last-modification timestamps separated by less
  than a second.  (Note: even in the most recent release, Perl cannot
  always match the file system’s timestamp resolution.)

  Generated configure scripts continue to run without Perl.

*** Autoconf users now need GNU M4 1.4.8 (2006) or later.
  Use of GNU M4 1.4.16 or later is recommended, as all earlier versions
  are known to have had serious bugs in the text-processing builtins
  on some, but not all, operating systems.  Autoconf’s own configure
  script will attempt to find a version of M4 that is not affected by
  these bugs.

  Note: Autoconf 2.70 and 2.71 include code that malfunctions with
  M4 1.4.6 or 1.4.7.  However, the only effect of the malfunction is
  that you will get a confusing error message if you run autoconf on
  a configure.ac that neglects to use AC_INIT or AC_OUTPUT.

  Generated 'configure' scripts continue to run without M4.

*** Some m4sh diversions have been renumbered.
  This will only affect macros that use m4_divert with numbered rather
  than named diversions, which has always been strongly discouraged
  both by the documentation and with warnings.

*** AC_FUNC_GETGROUPS and AC_TYPE_GETGROUPS no longer run test programs.
  These macros were testing for OS bugs that we believe are at least
  twenty years in the past.  Most operating systems are now trusted to
  provide an accurate prototype for getgroups in unistd.h, and to
  implement it as specified in POSIX.

  AC_FUNC_GETGROUPS still includes a short block-list of OSes with
  known, severe bugs in getgroups.  It can be overridden using
  config.site.  If you encounter a mistake in this list,
  please report it to bug-autoconf.

*** All internal uses of AC_EGREP_CPP and AC_EGREP_HEADER have been removed.
  These macros look for text matching a regular expression in the
  output of the C preprocessor.  Their use has been discouraged for
  many years, as they tend to be unreliable; it is better to find a
  way to use AC_COMPILE_IFELSE or AC_PREPROC_IFELSE instead.  We have
  finally taken our own advice.

  This change might break configure scripts that expected probes for
  ‘grep’ and/or the C preprocessor to happen as a side effect of an
  unrelated operation.  Such scripts can be fixed by adding
  AC_PROG_EGREP and/or AC_PROG_CPP in an appropriate place.

  The macros affected by this change are AC_C_STRINGIZE,
  AC_C_VARARRAYS, AC_FUNC_GETGROUPS, AC_FUNC_GETLOADAVG,
  AC_HEADER_TIOCGWINSZ, AC_PROG_GCC_TRADITIONAL, AC_TYPE_GETGROUPS,
  AC_TYPE_UID_T, and AC_XENIX_DIR. Many of these macros are themselves
  obsolete; if your configure script uses any of them, check whether
  it is actually needed.

** New features

*** Support for ensuring time_t is Y2038-safe
  configure can now ensure that time_t can represent moments in time
  after 18 January 2038, i.e. 2**31 - 1 seconds after the Unix epoch.
  On most “64-bit” systems this is true by default; the new feature
  is detection of systems where time_t is a 32-bit signed integer by
  default, *and* there is an alternative mode in which it is larger,
  in which case that mode will be enabled.

  In this release, all configure scripts that use AC_SYS_LARGEFILE
  gain a new command line option --enable-year2038.  When this option
  is used, the configure script will check for and enable support for
  a large time_t.

  This release also adds two new macros, AC_SYS_YEAR2038 and
  AC_SYS_YEAR2038_RECOMMENDED.  Both have all the effects of
  AC_SYS_LARGEFILE.  (This is because it is not possible to enlarge
  time_t without also enlarging off_t, on any system we are aware of.)

  AC_SYS_YEAR2038 additionally flips the default for --enable-year2038;
  a configure script that uses this macro will check for and enable
  support for a large time_t by default, but this can be turned off by
  using --disable-year2038.  AC_SYS_YEAR2038_RECOMMENDED goes even
  further, and makes the configure script fail on systems that do not
  seem to support timestamps after 18 January 2038 at all.  This
  failure can be suppressed by using --disable-year2038.

  Changing the size of time_t can change a library’s ABI.  Therefore,
  application and library builders should take care that all packages
  are configured with consistent use of --enable-year2038 or
  --disable-year2038, to ensure binary compatibility.  This is similar
  to longstanding consistency requirements with --enable-largefile and
  --disable-largefile.

  In this release, these macros only know how to enlarge time_t on two
  classes of systems: 32-bit MinGW, and any system where time_t can be
  enlarged by defining the preprocessor macro _TIME_BITS with the
  value 64.  At the time this NEWS entry was written, only GNU libc
  (version 2.34 and later) supported the latter macro.  Authors of
  other C libraries with a 32-bit time_t are encouraged to adopt
  _TIME_BITS, rather than inventing a different way to enlarge time_t.

*** AC_USE_SYSTEM_EXTENSIONS now enables C23 Annex F extensions
  by defining __STDC_WANT_IEC_60559_EXT__.

** Obsolete features and new warnings

*** Autoconf now quotes 'like this' instead of `like this'.
  Autoconf’s diagnostics now follow current GNU coding standards,
  which say that diagnostics in the C locale should quote 'like this'
  with plain apostrophes instead of the older GNU style `like this'
  with grave accent and apostrophe.

*** AC_PROG_GCC_TRADITIONAL no longer does anything.
  This macro has had no useful effect since GCC dropped support for
  traditional-mode compilation in version 3.3 (released in 2003), and
  the systems that needed it are also long obsolete.  It is now a
  compatibility synonym for AC_PROG_CC.

** Notable bug fixes

*** autom4te now uses fine-grained file timestamps
  Autoconf’s internal “autom4te” utility is now able to compare file
  modification timestamps with sub-second precision, when available.
  This eliminates a class of bugs where autom4te fails to regenerate
  an outdated file.  Automake 1.17 (forthcoming) is required for a
  complete fix.

*** AC_HEADER_STDBOOL, AC_CHECK_HEADER_STDBOOL are obsolescent and less picky.
  These macros are now obsolescent, as most programs can simply include
  stdbool.h unconditionally.  If you use these macros, they now accept
  a stdbool.h that exists but does nothing, so long as ‘bool’, ‘true’,
  and ‘false’ work anyway.  This is for compatibility with C23 and
  with C++.

*** AC_PROG_MKDIR_P now falls back on plain 'mkdir -p'.
  When AC_PROG_MKDIR_P cannot find a mkdir implementation that is
  known to lack race condition bugs, it now falls back on 'mkdir -p'
  instead of falling back on a relative path to install-sh, as the
  relative paths now seem to be a more important problem than the
  problems of ancient mkdir implementations with race condition bugs.
  See <https://savannah.gnu.org/support/?110740>.  The only ancient
  mkdir still supported is Solaris 10 /usr/bin/mkdir, and for that
  platform AC_PROG_MKDIR_P falls back on /opt/sfw/bin/mkdir which
  should work if it is installed; if not, you should avoid parallel
  'make' on that platform.

*** Better diagnostics for calling m4_warn() with a bad first argument
  Calling m4_warn with a first argument that doesn’t match any of the
  official warning categories now produces a sensible error message,
  instead of something that makes it look like there’s a bug in the
  guts of autom4te.  Also, the documentation has been adjusted in
  several places to make it clearer what the official warning
  categories are.

  Note: In Autoconf 2.69 and earlier, the manual said that [] and [all]
  could be used as the first argument to m4_warn.  This was incorrect,
  even at the time.

*** Improved compatibility with a wide variety of systems and tools
  including CheriBSD, Darwin (macOS), GNU Guix, OS/2, z/OS, Bash 5.2,
  the BusyBox shell and utilities, Clang/LLVM version 16, the upcoming
  GCC version 14, etc.

** Known bugs

*** AC_SYS_LARGEFILE and AC_SYS_YEAR2038 only work correctly in C mode.

  This is only a problem for configure scripts that invoke either
  macro while AC_LANG([something other than C]) is in effect, and
  will only be a *visible* problem on systems where support
  for large files and/or timestamps after 2038 are *available*
  but not enabled by default.

  This is the cause of the AC_SYS_LARGEFILE, AC_SYS_YEAR2038, and/or
  AC_SYS_YEAR2038_RECOMMENDED testsuite failures on some systems.
  See <https://savannah.gnu.org/support/index.php?110983> for details
  and a workaround.

* Noteworthy changes in release 2.71 (2021-01-28) [stable]

** Bug fixes, including:

*** Compilers that support C99 but not C2011 are detected correctly.

*** Compatibility improved with clang and Oracle C++.

*** Compatibility restored with automake's rules for regenerating configure.

*** Compatibility restored with old versions of std-gnu11.m4.

  Packages that wish to maintain compatibility with Autoconf 2.69 or
  older, should update their copy of std-gnu11.m4 from Gnulib as soon
  as practical, as the compatibility code bulks up the configure script.

  Packages that require Autoconf 2.70 can drop this file entirely.

* Noteworthy changes in release 2.70 (2020-12-08) [stable]

** Backward incompatibilities:

*** Warnings about obsolete constructs are now on by default.

  These warnings can be turned off with ‘-Wno-obsolete’.

  Many of these warnings advise maintainers to run autoupdate.
  Be aware that autoupdate cannot solve all backward compatibility
  problems, and cannot completely solve all of the problems it does
  address.  A configure script edited by autoupdate is likely to
  need further manual fix-ups.

*** Many macros have become pickier about argument quotation.

  If you get a shell syntax error from your generated configure
  script, or seemingly impossible misbehavior (e.g. entire blocks of
  the configure script not getting executed), check first that all
  macro arguments are properly quoted. The “M4 Quotation” section of
  the manual explains how to quote macro arguments properly.

  It is unfortunately not possible for autoupdate to correct
  quotation errors.

*** Many macros no longer AC_REQUIRE as many other macros as they used to.

  This can expose several classes of latent bugs.  These are the ones
  we know about:

   - Make sure to explicitly invoke all of the macros that set result
     variables used later in the configure script, or in generated
     Makefiles.

   - Autoconf macros that use AC_REQUIRE are not safe to use in shell
     control-flow constructs that appear outside of macros defined by
     AC_DEFUN.  Use AS_IF, AS_CASE, etc. instead.  (See the
     “Prerequisite Macros” section of the manual for details.)

     The set of macros that use AC_REQUIRE internally may change from
     release to release.  The only macros that are guaranteed *not* to
     use AC_REQUIRE are the macros for acting on the results of a
     test: AC_DEFINE, AC_SUBST, AC_MSG_*, AC_CACHE_CHECK, etc.

   - AC_REQUIRE cannot be applied to macros that need to be used with
     arguments.  Instead, invoke the macro normally, with its arguments.

*** More macros use config.sub and config.guess internally.

  As a consequence of improved support for cross compilation (see below),
  more macros now use the auxiliary scripts ‘config.sub’ and ‘config.guess’.
  If you use any of the affected macros, these scripts must be available
  when your configure script is run, even if you have no intention of
  ever cross-compiling your program.

  autoreconf will issue an error if any auxiliary scripts are needed but
  cannot be found.  (It is not currently possible to make autoconf
  itself issue this error.)

  ‘autoreconf --install’ will add ‘config.sub’, ‘config.guess’, and
  ‘install-sh’ to your source tree if they are needed.  If you are
  using Automake, scripts added to your tree by ‘autoreconf --install’
  will automatically be included in the tarball produced by ‘make dist’;
  otherwise, you will need to arrange for them to be distributed
  yourself.

  See the “Input” section of the manual for more detail, including
  where to get the auxiliary scripts that may be needed by autoconf macros.

*** Setting CC to a C++ compiler is no longer supported.

  The C and C++ languages have diverged enough that we can no longer
  guarantee that test C programs will be processed as intended by a
  C++ compiler.  In this release, configure will proceed anyway, but
  many test results will be incorrect.  In a future release, we may
  make AC_PROG_CC error out if it detects that CC is a C++ compiler.

  See the “Language Choice” section of the manual for instructions on
  how to write configure scripts for C++ programs, and for programs
  with code in more than one language.

*** Running configure tests with warnings promoted to errors is not supported.

  For instance, setting ‘CC="gcc -Werror"’ on the configure command
  line, or adding -Werror to CFLAGS early in the configure script when
  the compiler recognizes this option, is very likely to cause
  subsequent tests to fail.

  This has never been guaranteed to work; the code generated by
  AC_CHECK_FUNC, for instance, is incorrect by a strict reading of the
  original 1989 C standard, and has been ever since that macro was
  introduced.  Problems are more likely with newer, pickier compilers.

  To enable compiler warnings and/or warnings-as-errors mode for your
  own code, we currently recommend a dedicated Makefile variable
  (e.g. ‘WARN_CFLAGS’) that is set by AC_SUBST when appropriate.
  The Gnulib ‘warnings’ and ‘manywarnings’ modules can help with this.
  We plan to add core support for probing for useful sets of compiler
  warnings in a future release.

*** Including confdefs.h manually may cause test failures.

  This has never been necessary; confdefs.h is automatically included
  at the beginning of all test programs (by AC_LANG_SOURCE).  Because
  of the way confdefs.h is generated and used, it is not practical to
  give it a multiple inclusion guard.  Therefore, if you include it
  yourself, all of its definitions will be scanned twice.

  Historically this has not been a problem, because confdefs.h only
  makes macro definitions, and the C standard allows redefinitions
  of macros as long as they’re exactly the same, but newer, pickier
  compilers may complain anyway (see for instance GCC bug 97998).

*** Older versions of automake and aclocal (< 1.8) are no longer supported.

*** AC_CONFIG_SUBDIRS no longer directly supports Cygnus configure.

  If you are still using an Autoconf script to drive configuration of
  a multi-package build tree where some subdirectories use Cygnus
  configure, copy or link $ac_aux_dir/configure into each subdirectory
  where it is needed.  Please also contact us; we were under the
  impression nobody used this very old tool anymore.

*** AC_CHECK_HEADER and AC_CHECK_HEADERS only do a compilation test.

  This completes the transition from preprocessor-based header tests
  begun in Autoconf 2.56.

  The double test that was the default since Autoconf 2.64 is no
  longer available.  You can still request a preprocessor-only test
  by specifying [-] as the fourth argument to either macro, but this
  is now deprecated.  If you really need that behavior use
  AC_PREPROC_IFELSE.

*** AC_INCLUDES_DEFAULT assumes an ISO C90 compliant C implementation.

  Specifically, it assumes that the ISO C90 header <stddef.h>
  is available, without checking for it, and it does not include
  the pre-standard header <memory.h> at all.  If the POSIX header
  <strings.h> exists, it will be included, without first testing
  whether both <string.h> and <strings.h> can be included in the
  same source file.

  AC_INCLUDES_DEFAULT still checks for the existence of <stdlib.h>,
  <string.h>, and <stdio.h>, because these headers may not exist
  in a “freestanding environment” (a compilation mode intended for OS
  kernels and similar, where most of the features of the C library are
  optional).  Most programs need not use ‘#ifdef HAVE_STDLIB_H’ etc in
  their own code.

  For compatibility’s sake, the C preprocessor macro STDC_HEADERS
  will be defined when both <stdlib.h> and <string.h> are available;
  however, <stdarg.h> and <float.h> are no longer checked for
  (these, like <stddef.h>, are required to exist in a freestanding
  environment).  New code should not refer to this macro.

  Future releases of Autoconf may reduce the set of headers checked
  for by AC_INCLUDES_DEFAULT.

*** AS_ECHO and AS_ECHO_N unconditionally use ‘printf’.

  This is substantially simpler, more reliable, and, in most cases,
  faster than attempting to use ‘echo’ at all.  However, if ‘printf’
  is not a shell builtin, configure scripts will run noticeably
  slower, and if ‘printf’ is not available at all, they will crash.
  The only systems where this is known to be a problem are extremely
  old, and unlikely to be able to handle modern C programs for other
  reasons (e.g. not having a C90-compliant compiler at all).

*** Configure scripts require support for $( ... ) command substitution.

  This POSIX shell feature is approximately the same age as
  user-defined functions, but there do exist shells that support
  functions and not $( ... ), such as Solaris 10 /bin/sh.

  Configure scripts will automatically locate a shell that supports
  this feature and re-execute themselves with it, if necessary, so
  the new requirement should be transparent to most users.

  In this release, most of Autoconf’s code still uses the older `...`
  notation for command substitution.

*** AC_INIT now trims extra white space from its arguments.

  For instance, AC_INIT([  GNU  Hello  ], [1.0]) will set PACKAGE_NAME
  to “GNU Hello”.

*** Macros that take whitespace-separated lists as arguments
    now always expand macros within those arguments.

  Formerly, these macros would *usually* expand those arguments, but
  the behavior was not reliable nor was it consistent between autoconf
  and autoheader.

  Macro expansion within these arguments is deprecated; if expansion
  changes the list, a warning in the “obsolete” category will be
  emitted.  Note that ‘dnl’ is a macro.  Putting ‘dnl’ comments inside
  any argument to an Autoconf macro is, in general, only supported
  when that argument takes more Autoconf code (e.g. the ACTION-IF-TRUE
  argument to AC_COMPILE_IFELSE).

  The affected macros are AC_CHECK_FILES, AC_CHECK_FUNCS,
  AC_CHECK_FUNCS_ONCE, AC_CHECK_HEADERS, AC_CHECK_HEADERS_ONCE,
  AC_CONFIG_MACRO_DIRS, AC_CONFIG_SUBDIRS, and AC_REPLACE_FUNCS.

*** AC_FUNC_VFORK no longer ignores a signal-handling bug in Solaris 2.4.

  This bug was being ignored because Emacs wanted to use ‘vfork’ on
  Solaris 2.4 anyway, but current versions of Emacs have dropped
  support for Solaris 2.4.  Most programs will want to avoid ‘vfork’
  on this OS because of this bug.

*** AC_FUNC_STRERROR_R assumes strerror_r is unavailable if it’s not declared.

  The fallback technique it used to probe strerror_r’s return type
  when the function was present in the C library, but not declared by
  <string.h>, was fragile and did not work at all when cross-compiling.
  The systems where this fallback was necessary were all obsolete.

  Programs that use AC_FUNC_STRERROR_R should make sure to test the
  preprocessor macro HAVE_DECL_STRERROR_R before using strerror_r at all.

*** AC_OPENMP can’t be used if you have files named ‘mp’ or ‘penmp’.

  Autoconf will now issue an error if AC_OPENMP is used in a configure
  script that’s in the same directory as a file named ‘mp’ or ‘penmp’.
  Configure scripts that use AC_OPENMP will now error out upon
  encountering files with these names in their working directory
  (e.g. when the build directory is separate from the source directory).

  If you have files with these names at the top level of your source
  tree, we recommend either renaming them or moving them into a
  subdirectory.  See the documentation of AC_OPENMP for further
  explanation.

** New features

*** Configure scripts now support a ‘--runstatedir’ option.

  This defaults to ‘${localstatedir}/run’.  It can be used, for
  instance, to place per-process temporary runtime files (such as pid
  files) into ‘/run’ instead of ‘/var/run’.

*** autoreconf will now run gtkdocize and intltoolize when appropriate.

*** autoreconf now recognizes AM_GNU_GETTEXT_REQUIRE_VERSION.

  This macro can be used with gettext 0.19.6 or later to specify
  a *minimum* version requirement for gettext, instead of the *fixed*
  version requirement specified by AM_GNU_GETTEXT_VERSION.

*** autoheader handles secondary config headers better.

  It is no longer necessary to duplicate AC_DEFINE templates in the
  main configuration header for autoheader to notice them.

*** AC_PROG_CC now enables C2011 mode if the compiler supports it.

  If not, it will fall back to C99 and C89, as before.  Similarly,
  AC_PROG_CXX now enables C++2011 if available, falling back on C++98.

*** New macro AC_C__GENERIC tests for C2011 _Generic support.

*** AC_C_VARARRAYS has been aligned with C2011.

  It now defines __STDC_NO_VLA__ if variable-length arrays are not
  supported but the compiler does not define __STDC_NO_VLA__.

  For backward compatibility with Autoconf 2.61-2.69 AC_C_VARARRAYS
  still defines HAVE_C_VARARRAYS, but this result macro is obsolescent.

*** New macro AC_CONFIG_MACRO_DIRS.

  This macro can be used more than once and accepts a list of
  directories to search for local M4 macros.  With Automake 1.13 and
  later, use of this macro eliminates a reason to use ACLOCAL_AMFLAGS
  in Makefile.am.

  The older AC_CONFIG_MACRO_DIR, which could only be used once, is
  still supported but considered deprecated.

*** AC_USE_SYSTEM_EXTENSIONS knows about more extensions to enable.

  System extensions will now be enabled on HP-UX, macOS, and MINIX.
  Optional ISO C library components (e.g. decimal floating point) will
  also be enabled.

*** New compatibility macro AC_CHECK_INCLUDES_DEFAULT.

  This macro runs the checks normally performed as a side-effect by
  AC_INCLUDES_DEFAULT, if they haven’t already been done.  Autoupdate
  will replace certain obsolete constructs, whose only remaining
  useful effect is to trigger those checks, with this macro.  It is
  unlikely to be useful otherwise.

*** AC_REQUIRE_AUX_FILE has been improved.

  Configure scripts now check, on startup, for the availability of all
  the aux files that were mentioned in an AC_REQUIRE_AUX_FILE
  invocation.  This should help prevent certain classes of packaging
  errors.

  Also, it is no longer necessary for third-party macros that use
  AC_REQUIRE_AUX_FILE to mention AC_CONFIG_AUX_DIR_DEFAULT.  However,
  if you are using AC_CONFIG_AUX_DIR_DEFAULT *without* also using
  AC_REQUIRE_AUX_FILE, please start using AC_REQUIRE_AUX_FILE to
  specify the aux files you actually need, so that the check can be
  effective.

*** AC_PROG_LEX has an option to not look for yywrap.

  AC_PROG_LEX now takes one argument, which may be either ‘yywrap’ or
  ‘noyywrap’.  If it is ‘noyywrap’, AC_PROG_LEX will only set LEXLIB
  to ‘-lfl’ or ‘-ll’ if a scanner that defines both main and yywrap
  itself still needs something else from that library.  On the other
  hand, if it is ‘yywrap’, AC_PROG_LEX will fail (setting LEX to ‘:’
  and LEXLIB to nothing) if it can’t find a library that defines yywrap.

  In the absence of arguments, AC_PROG_LEX’s behavior is bug-compatible
  with 2.69, which did neither of the above things (see the manual for
  details).  This mode is deprecated.

  We encourage all programs that use AC_PROG_LEX to use the new
  ‘noyywrap’ mode, and to define yywrap themselves, or use %noyywrap.
  The yywrap function in lib(f)l is trivial, and self-contained
  scanners are easier to work with.

** Obsolete features and new warnings

*** Use of the long-deprecated name ‘configure.in’ for the autoconf
    input file now elicits a warning in the “obsolete” category.

*** Use of the undocumented internal shell variables $as_echo and
    $as_echo_n now elicits a warning in the “obsolete” category.
    The macros AS_ECHO and AS_ECHO_N should be used instead.

*** autoconf will now issue warnings (in the “syntax” category)
    if the input file is missing a call to AC_INIT and/or AC_OUTPUT.

*** autoconf will now issue warnings (in the “syntax” category)
    for a non-literal URL argument to AC_INIT, and for a TARNAME
    argument to AC_INIT which is either non-literal or contains
    characters that should not be used in file names (e.g. ‘*’).

*** AC_PROG_CC_STDC, AC_PROG_CC_C89, AC_PROG_CC_C99 are now obsolete.

  Applications should use AC_PROG_CC.

*** AC_HEADER_STDC and AC_HEADER_TIME are now stubs.

  They still define the C preprocessor macros STDC_HEADERS and
  TIME_WITH_SYS_TIME, respectively, but they no longer check for the
  ancient, non-ISO-C90 compliant systems where formerly those macros
  would not be defined.  Autoupdate will remove them.

  These macros were already labeled obsolete in the manual.

*** AC_DIAGNOSE, AC_FATAL, AC_WARNING, and _AC_COMPUTE_INT are now
    replaced with modern equivalents by autoupdate.

  These macros were already labeled obsolete in the manual.

*** AC_CONFIG_HEADER is now diagnosed as obsolete, and replaced with
    AC_CONFIG_HEADERS by autoupdate.

  This macro has been considered obsolete for many years and was not
  documented at all.

*** The macro AC_OBSOLETE is obsolete.

  Autoupdate will replace it with m4_warn([obsolete], [explanation]).
  If possible, macros using AC_OBSOLETE should be converted to use
  AU_DEFUN or AU_ALIAS instead, which enables autoupdate to replace
  them, but this has to be done by hand and is not always possible.

  This macro has been considered obsolete for many years, but was not
  officially declared as such.

*** Man pages for config.guess and config.sub are no longer provided.

  They were moved to the master source tree for config.guess and
  config.sub.

** Notable bug fixes

*** Compatible with current Automake, Libtool, Perl, Texinfo, and shells.

  All of autoconf’s tools and generated scripts, and the build process
  and testsuite for autoconf itself, have been tested to work
  correctly with current versions of Automake, Libtool, Perl, Texinfo,
  bash, ksh93, zsh, and FreeBSD and NetBSD /bin/sh.

  Generated configure scripts are expected to work reliably with an
  even wider variety of shells, including BusyBox sh and various
  proprietary Unixes’ /bin/sh, as long as they are minimally compliant
  with the Unix95 shell specification.  Notably, support for
  shell-script functions and the ‘printf’ builtin are required.

*** Checks compatible with current language standards and compilers.

  Many individual macros have been improved to accommodate changes in
  recent versions of the C and C++ language standards, and new
  features and quirks of commonly used compilers (both free and
  proprietary).

*** Improved support for cross compilation.

  Many individual macros have been improved to produce more accurate
  results when cross-compiling.

*** Improved robustness against unusual build environments.

  Many bugs have been fixed where generated configure scripts would
  fail catastrophically under unusual conditions, such as stdout being
  closed, or $TMPDIR not being an absolute path, or the root directory
  being mentioned in $PATH.

*** AC_CHECK_FUNCS_ONCE and AC_CHECK_HEADERS_ONCE now support multiple
    programming languages.  They no longer perform all checks in the
    language active upon the first use of the macro.

*** AC_CHECK_DECL and AC_CHECK_DECLS will now detect missing declarations for
    library functions that are also Clang compiler builtins.

*** AC_PATH_X and AC_PATH_XTRA don’t search for X11 when cross-compiling.

  Libraries and headers found by running xmkmf or searching /usr/X11,
  /usr/X11R7, etc. are likely to belong to a native X11 installation
  for the build machine and to be inappropriate for cross compilation.

  To cross-compile programs that require X11, we recommend putting the
  headers and libraries for the host system in your cross-compiler’s
  default search paths.  Alternatively, use configure’s --x-includes
  and --x-libraries command line options to tell it where they are.

*** AS_IF’s if-false argument may be empty after macro expansion.

  This long-standing limitation broke configure scripts that used
  macros in this position that emitted shell code in 2.69 but no
  longer do, so we have lifted it.

*** AC_HEADER_MAJOR detects the location of the major, minor, and
    makedev macros correctly under glibc 2.25 and later.

*** AC_FC_LINE_LENGTH now documents the maximum portable length of
    “unlimited” Fortran source code lines to be 250 columns, not 254.

*** AC_INIT and AS_INIT no longer embed (part of) the path to the
    source directory in generated files.

  We believe this was the only case where generated file contents
  could change depending on the environment outside the source tree
  itself.  If you find any other cases please report them as bugs.

*** config.log properly escapes arguments in the header comment.

*** config.status --config output is now quoted in a more readable fashion.

** Autotest enhancements

*** Autotest provides a new macro AT_DATA_UNQUOTED, similar to AT_DATA
    but processing variable substitutions, command substitutions and
    backslashes in the contents argument.

*** AC_CONFIG_TESTDIR will automatically pass EXEEXT to a testsuite (via
    the atconfig file).

*** AT_TESTED arguments can use variable or command substitutions, including
    in particular $EXEEXT

*** New macros AT_PREPARE_TESTS, AT_PREPARE_EACH_TEST, and AT_TEST_HELPER_FN.

   These provide an official way to define testsuite-specific
   initialization code and shell functions.

* Noteworthy changes in release 2.69 (2012-04-24) [stable]

** Autoconf now requires perl 5.6 or better (but generated configure
   scripts continue to run without perl).

* Noteworthy changes in release 2.68b (2012-03-01) [beta]
  Released by Eric Blake, based on git versions 2.68.*.

** Autoconf-generated configure scripts now unconditionally re-execute
   themselves with $CONFIG_SHELL, if that's set in the environment.

** The texinfo documentation no longer specifies "front-cover" or
   "back-cover" texts, so that it may now be included in Debian's
   "main" section.

** Support for the Go programming language has been added.  The new macro
   AC_LANG_GO sets variables GOC and GOFLAGS.

** AS_LITERAL_IF again treats '=' as a literal.  Regression introduced in
   2.66.

** The macro AS_EXECUTABLE_P, present since 2.50, is now documented.

** Macros

- AC_PROG_LN_S and AS_LN_S now fall back on 'cp -pR' (not 'cp -p') if 'ln -s'
  does not work.  This works better for symlinks to directories.

- New macro AC_HEADER_CHECK_STDBOOL.

- New and updated macros for Fortran support:

    AC_FC_CHECK_BOUNDS to enable array bounds checking
    AC_F77_IMPLICIT_NONE and AC_FC_IMPLICIT_NONE to disable implicit integer
    AC_FC_MODULE_EXTENSION to compute the Fortran 90 module name extension
    AC_FC_MODULE_FLAG for the Fortran 90 module search path flag
    AC_FC_MODULE_OUTPUT_FLAG for the Fortran 90 module output directory flag
    AC_FC_PP_SRCEXT for preprocessed Fortran source files extensions
    AC_FC_PP_DEFINE for the Fortran preprocessor define flag

* Noteworthy changes in release 2.68 (2010-09-22) [stable]
  Released by Eric Blake, based on git versions 2.67.*.

** AC_MSG_ERROR (and AS_ERROR) can once again be followed immediately by
   'dnl'.  Regression introduced in 2.66.

** AC_INIT again allows URLs with '?' for its BUG-REPORT argument.
   Regression introduced in 2.66.

** AC_REPLACE_FUNCS again allows a non-literal argument, such as a shell
   variable that expands to a list of functions to check.  Regression
   introduced in 2.66.

** AT_BANNER() with empty argument will cause visual separation from previous
   test category.

** The macros AC_PREPROC_IFELSE, AC_COMPILE_IFELSE, AC_LINK_IFELSE, and
   AC_RUN_IFELSE now warn if the first argument failed to use
   AC_LANG_SOURCE or AC_LANG_PROGRAM to generate the conftest file
   contents.  A new macro AC_LANG_DEFINES_PROVIDED exists if you have
   a compelling reason why you cannot use AC_LANG_SOURCE but must
   avoid the warning.

** The macro m4_define_default is now documented.

** Symlinked config.cache files are supported; configure now tries to
   update non-symlinked cache files atomically, so that concurrent configure
   runs do not leave behind broken cache files.  It is still unspecified
   which subset or union of results is cached though.

** Autotest testsuites should not contain long text lines any more, and be
   portable even when very many test groups are used.

** AT_CHECK semantics with respect to the Autotest variable $at_status and
   shell execution environment of the arguments are documented now.

** AC_FC_LIBRARY_LDFLAGS now tolerates output from newer gfortran.

** Newly obsolete macros
   The following macros have been marked obsolete.  New programs
   should use the corresponding Gnulib modules.  Gnulib not only
   detects a larger set of portability problems with these functions,
   but also provides complete workarounds.

     AC_FUNC_ERROR_AT_LINE  AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
     AC_FUNC_MKTIME  AC_FUNC_STRTOD


* Major changes in Autoconf 2.67 (2010-07-21) [stable]
  Released by Eric Blake, based on git versions 2.66.*.

** AC_CONFIG_SUBDIRS with more than one subdirectory at a time works again.
   Regression introduced in 2.66.

** AC_CHECK_SIZEOF of a pointer type works again.  Regression introduced in
   2.66.

** New macro AC_FC_LINE_LENGTH to accept long Fortran source code lines.

** AC_PREPROC_IFELSE now keeps the preprocessed output in the conftest.i
   file for inspection by the commands in the ACTION-IF-TRUE argument.

** AC_INIT again allows parentheses and other characters that are literal
   in single- or double-quoted strings, and in quoted and unquoted
   here-documents, for its PACKAGE and VERSION arguments.  Regression
   introduced in 2.66.

** autoreconf passes warning flags to new enough versions of aclocal.

** Running an Autotest testsuite in parallel mode no longer triggers a
   race condition that could cause the testsuite run to end early,
   fixing a sporadic failure in autoconf's own testsuite.  Bug present
   since introduction of parallel tests in 2.63b.


* Major changes in Autoconf 2.66 (2010-07-02) [stable]
  Released by Eric Blake, based on git versions 2.65.*.

** AC_FUNC_MMAP works in C++ mode again.  Regression introduced in 2.65.

** Use of m4_divert without a named diversion now issues a syntax warning,
   since it is seldom right to change diversions behind autoconf's back.

** The macros AC_TYPE_INT8_T, AC_TYPE_INT16_T, AC_TYPE_INT32_T, and
   AC_TYPE_INT64_T work again.  Regression introduced in 2.65.

** AC_PROG_INSTALL correctly uses 'shtool' again.  Regression introduced
   in 2.64.

** Autoconf should work on EBCDIC hosts.

** AC_CHECK_DECL and AC_CHECK_DECLS accept optional function argument types
   for overloaded C++ functions.

** AS_SET_CATFILE accepts nonliterals in its variable name argument now.

** Autotest testsuites accept an option --recheck to rerun tests that
   failed or passed unexpectedly during the last non-debug testsuite run.

** AC_ARG_ENABLE and AC_ARG_WITH now also accept '+' signs in '--enable-*'
   and '--with-*' arguments, converting them to underscores for the variable
   names.

** In configure scripts, loading CONFIG_SITE no longer searches PATH,
   and problems in loading the configuration site files are diagnosed.

** Autotest testsuites may optionally provide colored test results.

** The previously undocumented Autotest macros AT_ARG_OPTION and
   AT_ARG_OPTION_ARG have seen bug fixes and are documented now.
   AT_ARG_OPTION has been changed in that the negative of a long option
   --OPTION is now --no-OPTION rather than --noOPTION.

** The macro AS_LITERAL_IF is slightly more conservative; text
   containing shell quotes are no longer treated as literals.
   Furthermore, a new macro, AS_LITERAL_WORD_IF, adds an additional
   level of checking that no whitespace occurs in literals.

** The macros AS_TR_SH and AS_TR_CPP no longer expand their results.

** The following macros are now documented:
   AS_BOX

** New macro AC_FC_FIXEDFORM to accept fixed-form Fortran.


* Major changes in Autoconf 2.65 (2009-11-21) [stable]
  Released by Eric Blake, based on git versions 2.64.*.

** Autoconf is now licensed under the General Public License version 3
   or later (GPLv3+).  As with earlier versions, the license includes
   an exception clause so that you may release a configure script
   generated by autoconf under the license of your own program.

** New macros to support Objective C++.
   AC_PROG_OBJCXX  AC_PROG_OBJCXXCPP

** The following undocumented autoconf macros, removed in Autoconf 2.64,
   have been reinstated:
   AH_CHECK_HEADERS

   These macros are present only for backwards compatibility purposes.

** The macro AC_LANG_COMPILER no longer fails on embedded systems that
   lack fopen in the C library, such as AVR or RTEMS (regression
   introduced in 2.64).

** The AC_FC_FREEFORM macro no longer suffers from a whitespace bug that
   made it fail with some Fortran compilers (regression introduced in
   2.64).

** The AC_TYPE_UINT64_T and AC_TYPE_INT64_T macros have been fixed to no
   longer mistakenly select a 32-bit type on some compilers (bug present
   since macros were introduced in 2.59c).

** The AC_FUNC_MMAP macro has been fixed to be portable to systems like
   Cygwin (bug present since macro was introduced in 2.0).

** The following documented autotest macros are new:
   AT_CHECK_EUNIT

** The following m4sugar macros now quote their expansion:
   m4_toupper  m4_tolower

** The following m4sugar macros are new:
   m4_escape

** The m4sugar macro m4_text_wrap now copes with embedded quoting without
   requiring quadrigraphs.  For uses like AC_ARG_VAR([a], [[b c]]),
   this gives the intuitive behavior of "[b c]" in the output (2.63
   gave the output of "[b], [c]", and 2.64 encountered a failure).

** The '$tmp' temporary directory used in config.status is documented for
   public use now.

** config.status now provides a --config option to produce the configuration.

** Many cache variables used by Autoconf's macros are now documented.

** Configure scripts work better on DJGPP by avoiding a bug present in
   the DJGPP port of bash 2.04 in handling 'return' in a shell
   function (regression introduced in 2.64).

* Major changes in Autoconf 2.64 (2009-07-26) [stable]
  Released by Eric Blake, based on git versions 2.63b.*.

** Autoconf now requires GNU M4 1.4.6 or later.  Earlier versions of M4
   have a bug in regular expression handling that interferes with some
   of the speedups provided since Autoconf 2.63.  GNU M4 1.4.13 or
   later is recommended.

** AS_IF and AS_CASE have been taught to avoid syntax errors even when
   given arguments that expand to just whitespace.

** The following documented autoconf macros are new:
   AC_ERLANG_SUBST_ERTS_VER

** The autoheader tool now understands m4 macro arguments passed to
   AC_DEFINE and AC_DEFINE_UNQUOTED.

** Ensure AT_CHECK can support commands that include a # given with
   proper m4 quoting.  For shell comments, this is a new feature; for
   non-shell comments, this fixes a regression introduced in 2.63b.
   Additionally, AT_CHECK correctly supplies shell escapes for
   metacharacters occurring in m4 macro expansions within the expected
   stdout and stderr parameters.

** The macro AT_CHECK now understands the concept of hard failure.  If
   a test exits with an unexpected status 99, cleanup actions for the
   test are inhibited and the test is treated as a failure regardless
   of AT_XFAIL_IF.  It also understands the new directives
   ignore-nolog, stdout-nolog, and stderr-nolog.

** The following documented autotest macros are new:
   AT_CHECK_UNQUOTED  AT_FAIL_IF  AT_SKIP_IF

** The following documented m4sugar macros are new:
   m4_argn  m4_copy_force  m4_default_nblank  m4_default_nblank_quoted
   m4_ifblank  m4_ifnblank  m4_rename_force

** The autoconf testsuite now exercises all Erlang macros.

* Major changes in Autoconf 2.63b (2009-03-31) [beta]
  Released by Eric Blake, based on git versions 2.63.*.

** The manual is now shipped under the terms of the GNU FDL 1.3.

** AC_REQUIRE now detects the case of an outer macro which first expands
   then later indirectly requires the same inner macro.  Previously,
   this case led to silent out-of-order expansion (bug present since
   2.50); it now issues a syntax warning, and duplicates the expansion
   of the inner macro to guarantee dependencies have been met.  See
   the manual for advice on how to refactor macros in order to avoid
   the bug in earlier autoconf versions and avoid increased script
   size in the current version.

** AC_DEFUN_ONCE has improved semantics.  Previously, a macro declared
   with AC_DEFUN_ONCE warned on a second invocation; and out-of-order
   expansion was still possible.  Now, dependencies are guaranteed,
   and subsequent invocations are a silent no-op.  This makes
   AC_DEFUN_ONCE an ideal macro for silencing AC_REQUIRE warnings.

** The following macros are now defined with AC_DEFUN_ONCE.  This means
   a subtle change in semantics; previously, an AC_DEFUN macro could
   expand one of these macros multiple times or surround the macro
   inside shell conditional text to bypass the effects of these
   macros, but now the macro will expand exactly once, and prior to
   the start of any enclosing AC_DEFUN macro:
   AC_CANONICAL_BUILD  AC_CANONICAL_HOST  AC_CANONICAL_TARGET
   AC_HEADER_ASSERT  AC_PROG_INSTALL  AC_PROG_MKDIR_P
   AC_USE_SYSTEM_EXTENSIONS

** AC_LANG_ERLANG works once again (regression introduced in 2.61a).

** AC_HEADER_ASSERT is fixed so that './configure --enable-assert' no
   longer mistakenly disables assertions.

** AC_INIT now takes an optional fifth parameter that can be used to
   set AC_PACKAGE_URL, a URL for the package's home page; the URL is
   used in 'configure --help' and is also available via AC_DEFINE.

** Autotest testsuites accept an option --jobs[=N] for parallel testing.
   This feature is still in testing, and may not work on every
   platform, help in improving it would be appreciated.

** Autotest testsuites do not attempt to write startup error messages
   to the log file before that is opened (regression introduced in 2.63).

** Configure scripts now use shell functions.  This feature leads to
   smaller configure files and faster execution.

** Present But Cannot Be Compiled: Autoconf will now proceed with
   the compiler's result if a header is present but cannot be compiled.
   The warning is still printed, and you should really fix it by
   providing a fourth parameter to AC_CHECK_HEADER/AC_CHECK_HEADERS.

** Autoreconf added aclocal to the set of programs affected by the
   'autoreconf -I dir' option.

** The following documented m4sugar macros are new:
   m4_chomp  m4_chomp_all  m4_cleardivert  m4_curry  m4_default_quoted
   m4_esyscmd_s  m4_map_args  m4_map_args_pair  m4_map_args_sep
   m4_map_args_w  m4_set_map  m4_set_map_sep  m4_stack_foreach
   m4_stack_foreach_lifo  m4_stack_foreach_sep
   m4_stack_foreach_sep_lifo

** The following m4sugar macros are documented now, but in some cases
   with slightly different semantics than what the previous
   undocumented version had:
   m4_copy  m4_dumpdefs  m4_rename  m4_version_prereq

** The m4sugar macro m4_expand has been taught to handle unterminated
   comments and shell case statements.  As a result, it is used
   internally in more places, such as AC_DEFINE and AT_CHECK.  Most
   uses of AC_DEFINE and AT_CHECK should not behave any differently;
   however, it may be necessary to add double-quoting around
   unbalanced '(' where single-quoting used to be sufficient.

** The following documented m4sh macros are new:
   AS_INIT_GENERATED  AS_LINENO_PREPARE  AS_ME_PREPARE  AS_SET_STATUS
   AS_VAR_APPEND  AS_VAR_ARITH  AS_VAR_COPY

** The following m4sh macros are documented now, but in some cases
   with slightly different semantics than what the previous
   undocumented version had:
   AS_ECHO  AS_ECHO_N  AS_ESCAPE  AS_EXIT  AS_LITERAL_IF  AS_UNSET
   AS_VAR_IF  AS_VAR_POPDEF  AS_VAR_PUSHDEF  AS_VAR_SET  AS_VAR_SET_IF
   AS_VAR_TEST_SET  AS_VERSION_COMPARE

** The m4sh macros AS_IF and AS_CASE can now be used in shell lists.
   The responsibility for supplying a trailing newline now belongs to
   the call site, but since most users did not add dnl, this generally
   results in fewer empty lines in configure.


* Major changes in Autoconf 2.63 (2008-09-09) [stable]
  Released by Eric Blake, based on git versions 2.62.*.

** AC_C_BIGENDIAN does not mistakenly report "universal" for some
   bigendian hosts, a regression introduced with universal binary
   support in 2.62.

** AC_PATH_X now includes /lib64 and /usr/lib64 in its list of default
   library directories.

** AC_USE_SYSTEM_EXTENSIONS no longer conflicts with an external
   AC_DEFINE([__EXTENSIONS__]).  This fixes a regression introduced in
   2.62 when using macros such as AC_AIX that were made obsolete in
   favor of the more portable AC_USE_SYSTEM_EXTENSIONS.

** AC_CHECK_TARGET_TOOLS is usable in the non-cross-compile case.

** Newly obsolete macros
   The following macro has been marked obsolete, since current porting
   targets can safely assume C89 semantics that signal handlers return
   void.  We have no current plans to remove the macro.

     AC_TYPE_SIGNAL

** The macros m4_map and m4_map_sep now ignore any list elements
   consisting of just empty quotes, and m4_map_sep now expands its
   separator.  This fixes a regression in 2.62 when these macros were
   first documented, for the sake of clients expecting the semantics
   that these macros had prior to that time.  The new macros m4_mapall
   and m4_mapall_sep, along with extra quoting of the separator, can
   be used to get the semantics that m4_map_sep had in 2.62.

** Clients of m4_expand, such as AS_HELP_STRING and AT_SETUP, can now
   handle properly quoted but otherwise unbalanced parentheses (for
   some macros, this fixes a regression in 2.62).

** Two new quadrigraphs have been introduced: @{:@ for (, and @:}@ for ),
   allowing the output of unbalanced parentheses in more contexts.

** The following m4sugar macros are new:
   m4_cleardivert  m4_joinall  m4_mapall  m4_mapall_sep  m4_reverse
   m4_set_add  m4_set_add_all  m4_set_contains  m4_set_contents
   m4_set_delete  m4_set_difference  m4_set_dump  m4_set_empty
   m4_set_foreach  m4_set_intersection  m4_set_list  m4_set_listc
   m4_set_remove  m4_set_size  m4_set_union

** The following m4sugar macros now accept multiple arguments, as is the
   case with underlying m4:
   m4_defn  m4_popdef  m4_undefine

** The following m4sugar macros now guarantee linear scaling; they
   previously had linear scaling with m4 1.6 but quadratic scaling
   when using m4 1.4.x.  All macros built on top of these also gain
   the scaling improvements.
   m4_bmatch  m4_bpatsubsts  m4_case  m4_cond  m4_do  m4_dquote_elt
   m4_foreach  m4_join  m4_list_cmp  m4_map  m4_map_sep  m4_max
   m4_min  m4_shiftn

** AT_KEYWORDS once again performs expansion on its argument, such that
   AT_KEYWORDS([m4_if([$1], [], [default])]) no longer complains about
   the possibly unexpanded m4_if [regression introduced in 2.62].

** Config header templates '#undef UNDEFINED /* comment */' do not lead to
   nested comments any more; regression introduced in 2.62.


* Major changes in Autoconf 2.62 (2008-04-05) [stable]
  Released by Eric Blake, based on git versions 2.61a.*.

** Many optimizations have been applied to make overall execution faster.

** Autotest now makes use of shell functions.

** config.status now uses awk instead of sed also for config headers.

   - As a side effect, AC_DEFINE and AC_DEFINE_UNQUOTED now handle multi-line
     values, i.e., backslash-newline combinations are handled correctly.
     Further, for config headers, the total size of values is not limited by
     the POSIX length limit of text lines any more, only each single line.

** New config variable 'top_build_prefix'.

** New Autoconf macros:
   AC_AUTOCONF_VERSION  AC_OPENMP  AC_PATH_PROGS_FEATURE_CHECK

** AC_C_BIGENDIAN now supports universal binaries a la Mac OS X.

** AC_C_RESTRICT now prefers to #define 'restrict' to a variant spelling
   like '__restrict' if the variant spelling is available, as this is
   more likely to work when mixing C and C++ code.

** AC_CHECK_ALIGNOF's type argument T is now documented better: it must
   be a string of tokens such that "T y;" is a valid member declaration
   in a struct.

** AC_CHECK_SIZEOF now accepts objects as well as types: the general rule
   is that sizeof (X) works, then AC_CHECK_SIZEOF (X) should work.

** AC_CHECK_TYPE and AC_CHECK_TYPES now work on any C type-name; formerly,
   they did not work for function types.  In C++, they now work on any
   type-id that can be the operand of sizeof; this is similar to C,
   except it excludes anonymous struct and union types.  Formerly,
   some (but not all) C++ types involving anonymous struct and union
   were accepted, though this was not documented.

** AC_CONFIG_LINKS now prefers to link against files in the build tree
   if found, and it works to link against a file of the same name in
   the source tree, even if both trees coincide.

** AC_INIT no longer alters $@; regression introduced in 2.60.

** AC_USE_SYSTEM_EXTENSIONS now defines _ALL_SOURCE for Interix platforms.

** AS_HELP_STRING no longer underquotes its first argument; it also handles
   the case where the first argument contains single-quoted commas.
   For example, "AS_HELP_STRING([-a, [--arg[=foo]]], [bar])" produces:
     "  -a, --arg[=foo]         bar"
   Additionally, the macro now takes two additional arguments,
   indent-column and wrap-column; these should not normally be needed,
   but can be used to fine-tune how the output text is wrapped.

** AC_PROG_INSTALL now requires an install program that can install multiple
   files into a target directory.

** The command 'autoconf -' now correctly processes a file from stdin.

** 'autoreconf -m' now honors $MAKE.

** For all of the directory arguments for 'configure', such as '--prefix'
   or '--bindir', trailing slashes are stripped.  As an example, if
   tab completion in the user's shell appends trailing slashes, the
   command './configure --prefix=/usr/' will still result in an
   expanded libdir value of /usr/lib, not /usr//lib.

** 'configure --help=recursive' now works in read-only trees and from
   unconfigured build trees.

** If precious variables differ only in whitespace, then the cache consistency
   check warns instead of fails, and reuses the old value.

** AT_BANNER is now documented.

** AT_SETUP now handles macro expansions properly when calculating line
   length.

** Autotest now determines $srcdir correctly.

** Testsuites built by autotest now accept a -C/--directory=DIR option
   to adjust the working directory prior to creating files.

** Autoconf now requires GNU M4 1.4.5 or later.  Earlier versions of M4 have
   a bug in macro tracing that interferes with the interaction between
   Autoconf and Automake.  GNU M4 1.4.11 or later is recommended.  The
   configure search for a working M4 is improved.

** For portability with the eventual M4 2.0, macros should no longer use
   anything larger than $9 to refer to arguments.

** Documentation for m4sugar is improved.

   - The following macros were previously available as undocumented
     interfaces; the macros are now documented as stable interfaces.

     __oline__  m4_assert  m4_bmatch  m4_bpatsubsts  m4_car  m4_case
     m4_cdr  m4_default  m4_divert_once  m4_divert_pop  m4_divert_push
     m4_divert_text  m4_do  m4_errprintn  m4_fatal  m4_flatten
     m4_ifndef  m4_ifset  m4_ifval  m4_ifvaln  m4_location
     m4_n  m4_shiftn  m4_strip  m4_warn

   - The following macros were previously available as undocumented
     interfaces, but had bug fixes or semantic changes as part of this
     release.  Packages that relied on the undocumented behavior
     should be analyzed to make sure they will still work with the
     new documented behavior.

     m4_cmp  m4_list_cmp  m4_join  m4_map  m4_map_sep  m4_sign
     m4_text_box  m4_text_wrap  m4_version_compare

   - The m4_wrap macro used to have unspecified order, but now
     guarantees FIFO order.  m4_wrap_lifo was added to guarantee LIFO
     order.

   - Packages using the undocumented m4sugar macro m4_PACKAGE_VERSION
     should consider using the new AC_AUTOCONF_VERSION instead.

   - m4sugar macros that are not documented in the manual are still
     deemed experimental, and should not be used outside of Autoconf.

** The m4sugar macros m4_append and m4_append_uniq, first documented in
   2.60, have been fixed to treat both the string and the separator
   arguments consistently with regards to quoting.  Prior to this fix,
   m4_append_uniq could mistakenly duplicate entries if the expansion
   of the separator resulted in a different string (for example, if it
   contained quotes, a comma, or a macro name).  However, it means
   that programs previously using
     m4_append([name], [string], [[, ]])
   are now using a four-character separator instead of the intended
   comma and space.  If you need portability to earlier versions of
   Autoconf, you can insert the following snippet after AC_INIT but
   before any other macro expansions, to enforce the new semantics:
     m4_pushdef([m4_append], [m4_define([$1],
	   m4_ifdef([$1], [m4_defn([$1])[$3]])[$2])])
   Additionally, m4_append_uniq now takes optional parameters that can
   be used to take action depending on whether anything was appended,
   and warns if a non-empty separator occurs within the string being
   appended, since that can lead to duplicates.

** The following m4sugar macros are new:
   m4_append_uniq_w  m4_apply  m4_combine  m4_cond  m4_count
   m4_dquote_elt  m4_echo  m4_expand  m4_ignore  m4_make_list  m4_max
   m4_min  m4_newline  m4_shift2  m4_shift3  m4_unquote  m4_wrap_lifo

** Warnings are now generated by default when an installer invokes
   'configure' with an unknown --enable-* or --with-* option.
   These warnings can be disabled with the new AC_DISABLE_OPTION_CHECKING
   macro, or by invoking 'configure' with --disable-option-checking.

** Existing obsolete macros
   The documentation for the following macros is adjusted to make it
   more clear that they have previously been marked obsolete, as their
   functionality can be accomplished by other macros.  We have no
   current plans to remove them from Autoconf.

     AC_ENABLE  AC_STRUCT_ST_BLKSIZE  AC_STRUCT_ST_RDEV  AC_WITH

** Newly obsolete macros
   The following macros have been marked obsolete, as they only
   perform a subset of AC_USE_SYSTEM_EXTENSIONS.  We have no current
   plans to remove them.

     AC_AIX  AC_GNU_SOURCE  AC_ISC_POSIX  AC_MINIX

** AC_C_LONG_DOUBLE is obsolescent.
   The documentation now says that AC_C_LONG_DOUBLE is obsolescent: it
   tests for problems that are so old that it is no longer of
   practical importance on current systems.  New programs need not use
   AC_C_LONG_DOUBLE.  We have no current plans to remove it.

** AC_DIAGNOSE, AC_WARNING, and AC_FATAL are obsolescent.
   The documentation now favors the use of M4sugar macros m4_warn and
   m4_fatal, since the naming makes it more obvious that the
   diagnostics are associated with M4 expansion (ie. when running
   'autoconf'), and offers less confusion with the AC_MSG_ERROR,
   AC_MSG_FAILURE, and AC_MSG_WARN macros which manage diagnostics
   when running 'configure'.  We have no current plans to remove these
   macros.


* Major changes in Autoconf 2.61a (2006-12-11)

** AC_FUNC_FSEEKO was broken in 2.61; it didn't make fseeko and ftello visible
   on many platforms.  This has been fixed.

** AC_FUNC_SETVBUF_REVERSED is now obsolete.  It is still defined for backward
   compatibility but it does nothing.  The macro was already
   obsolescent, as the last systems to have the problem were those
   based on SVR2, which became obsolete in 1987.  The macro had bugs
   on some modern systems and could no longer be maintained reliably
   due to lack of ancient systems to test it on.

** config.status now uses awk instead of sed for most substitutions, for speed.

   - As a side effect multi-line values of substituted variables no
     longer have a small limit in total size, though for portability
     each line should not exceed the POSIX length limit for text lines.

   - It is now documented that Makefile.in should not contain
     overlapping variable occurrences, e.g., @VAR1@VAR2@.
     Autoconf's behavior was always iffy in such cases, and the
     awk implementation has changed the behavior.

** Many uses of 'echo' have been rewritten so that Autoconf-generated
   scripts have fewer problems with strings or file names containing
   embedded special characters such as backslash or leading "-".  This
   was implemented by using 'printf '%s\n' "$foo"' instead of 'echo
   "$foo"' when printf works.  Due to the implementation technique
   used, Autoconf-generated scripts now run considerably more slowly
   on ancient implementations lacking printf.  However, this should
   not be a problem, since Autoconf-generated scripts in practice
   invariably find a more-modern shell these days.


* Major changes in Autoconf 2.61 (2006-11-17)

** New macros AC_C_FLEXIBLE_ARRAY_MEMBER, AC_C_VARARRAYS.

** AC_ARG_ENABLE and AC_ARG_WITH now allow '.' in feature and package names.


* Major changes in Autoconf 2.60b (2006-10-22)

** BIN_SH
  Autoconf-generated shell scripts no longer export BIN_SH, due to
  configuration hassles with this.  Installers who need BIN_SH in
  their environment should set it before invoking 'configure' and
  'make'.  As far as we know, this affects only Unixware installations.

** Obsolescent macros
  The documentation now says that the following macros are obsolescent,
  as they are superseded by Gnulib:

    AC_FUNC_FNMATCH  AC_FUNC_FNMATCH_GNU  AC_FUNC_GETLOADAVG
    AC_REPLACE_FNMATCH

  New programs should use the Gnulib counterparts of these macros.
  We have no current plans to remove them from Autoconf.

** AC_COMPUTE_INT no longer caches or reports results.

** AC_CHECK_DECL now also works with aggregate objects.

** AC_USE_SYSTEM_EXTENSIONS now defines _TANDEM_SOURCE for NonStop platforms.

** GNU M4 1.4.7 or later is now recommended.

** m4_mkstemp
  New M4sugar macro, which is more secure than the POSIX M4 maketemp.

** m4_maketemp
  Now an alias for m4_mkstemp.

* Major changes in Autoconf 2.60a (2006-08-25)

** GNU M4 1.4.6 or later is now recommended.

** The check for C99 now tests for varargs macros, as documented.
  It also tests that the preprocessor supports 64-bit integers.

** Autoconf now uses constructs like "#ifdef HAVE_STDLIB_H" rather than
  "#if HAVE_STDLIB_H", so that it now works with "gcc -Wundef -Werror".

** The functionality of the undocumented _AC_COMPUTE_INT is now provided
  by a public and documented macro, AC_COMPUTE_INT.  The parameters to the
  two macros are different, so autoupdate will not change the old private name
  to the new one.  _AC_COMPUTE_INT may be removed in a future release.

** AC_TYPE_LONG_LONG_INT and AC_TYPE_UNSIGNED_LONG_LONG_INT now require
   that long long types be at least 64 bits wide, as C99 and tradition
   requires.  Formerly, they accepted implementations of any width.


* Major changes in Autoconf 2.60

  Released 2006-06-23, by Ralf Wildenhues.

** Autoconf no longer depends on whether m4wrap is FIFO (as POSIX requires)
  or LIFO (as in GNU M4 1.4.x).  GNU M4 2.0 is expected to conform to POSIX
  here, so m4wrap/m4_wrap users should no longer depend on LIFO behavior.

** Provide a way to turn off warnings about the changed directory variables.

* Major changes in Autoconf 2.59d

  Released 2006-06-05, by Ralf Wildenhues.

** GNU make now recommended for VPATH builds
  INSTALL now suggests VPATH builds (e.g., "sh ../srcdir/configure")
  only if you use GNU make.  In practice, other 'make' implementations
  have too many subtle incompatibilities in their support for VPATH.
  Many packages (including Autoconf itself) are portable to other
  'make' implementations, but some packages are not, and recommending
  GNU make keeps the installation instructions simpler.

** Even more safety checks for the new Directory variables:
  Warn about suspicious '${datarootdir}' found in config files output.

** AC_TRY_COMMAND, AC_TRY_EVAL, ac_config_guess, ac_config_sub, ac_configure
  These never-documented macros and variables have been marked with
  comments saying that they may be removed in a future release,
  because their use can lead to unintended code being executed.
  If you need functionality that only these macros or variables
  currently supply, please write bug-autoconf@gnu.org.

** AC_SUBST, AC_DEFINE
  Literal arguments to these are passed to m4_pattern_allow now.

** AC_PROG_CC_STDC
  Passing 'ac_cv_prog_cc_stdc=no' to 'configure' now sets ac_cv_prog_cc_c99
  and ac_cv_prog_cc_c89 to 'no' as well, for backward compatibility with
  obsolete K&R tests in the Automake test suite.

** AC_PROG_CXX_C_O
  New macro.

** AC_PROG_MKDIR_P
  New macro.

** AS_MKDIR_P
  Now more robust with special characters in file names, or when
  multiple processes create the same directory at the same time.

** Obsolescent macros
  The documentation now says that the following macros are obsolescent:
  they test for problems that are so old that they are no longer of
  practical importance on current systems.

    AC_C_BACKSLASH_A       AC_FUNC_MEMCMP            AC_HEADER_DIRENT
    AC_C_CONST             AC_FUNC_SELECT_ARGTYPES   AC_HEADER_STAT
    AC_C_PROTOTYPES        AC_FUNC_SETPGRP           AC_HEADER_STDC
    AC_C_STRINGIZE         AC_FUNC_SETVBUF_REVERSED  AC_HEADER_SYS_WAIT
    AC_C_VOLATILE          AC_FUNC_STAT              AC_HEADER_TIME
    AC_FUNC_CLOSEDIR_VOID  AC_FUNC_STRFTIME          AC_ISC_POSIX
    AC_FUNC_GETPGRP        AC_FUNC_UTIME_NULL        AC_PROG_GCC_TRADITIONAL
    AC_FUNC_LSTAT          AC_FUNC_VPRINTF           AC_STRUCT_TM

  New programs need not use these macros.  We have no current plans to
  remove them.

** autoreconf
  For compatibility with future Libtool 2.0, autoreconf will invoke
  libtoolize with the option '--ltdl' now, if LT_CONFIG_LTDL_DIR is
  used.

* Major changes in Autoconf 2.59c

  Released 2006-04-12, by Ralf Wildenhues.

** The configure command now redirects standard input from /dev/null,
  to help avoid problems with subsidiary commands that might mistakenly
  read standard input.  AS_ORIGINAL_STDIN_FD points to the original
  standard input before this redirection, if you really want configure to
  read from standard input.

** Directory variables adjusted to recent changes in the GNU Coding Standards.
  The following directory variables are new:

    datarootdir   read-only architecture-independent data root [PREFIX/share]
    localedir     locale-specific message catalogs [DATAROOTDIR/locale]
    docdir        documentation root [DATAROOTDIR/doc/PACKAGE]
    htmldir       html documentation [DOCDIR]
    dvidir        dvi documentation [DOCDIR]
    pdfdir        pdf documentation [DOCDIR]
    psdir         ps documentation [DOCDIR]

  The following variables have new default values:

    datadir       read-only architecture-independent data [DATAROOTDIR]
    infodir       info documentation [DATAROOTDIR/info]
    mandir        man documentation [DATAROOTDIR/man]

  This means that if you use any of '@datadir@', '@infodir@', or
  '@mandir@' in a file, you will have to ensure '${datarootdir}' is
  defined in this file.  As a temporary measure, if any of those are
  found but no mention of 'datarootdir', the substitutions will be
  replaced with values that do not contain '${datarootdir}', and a
  warning will be issued.

** @top_builddir@ is now a dir name: it is always nonempty and doesn't have
  a trailing slash.  Similar change will be made to ac_top_builddir in a
  future release; the old style value, which matches (../)*, is (and will
  continue to be) available as ac_top_build_prefix.

** AC_C_TYPEOF
  New macro to check for support of 'typeof' syntax a la GNU C.

** AC_CHECK_DECLS_ONCE, AC_CHECK_FUNCS_ONCE, AC_CHECK_HEADERS_ONCE
  New "once-only" variants of commonly-used macros, to make 'configure'
  smaller and faster in common cases.

** AC_FUNC_STRTOLD
  New macro to check for strtold with C99 semantics.

** AC_HEADER_ASSERT
  New macro that lets builder disable assertions at 'configure'-time.

** AC_PATH_X
  Now checks for X11/Xlib.h and XrmInitialize (X proper) rather than
  X11/Intrinsic.h and XtMalloc (Xt).

** AC_PRESERVE_HELP_ORDER
  New macro that causes 'configure' to display help strings for AC_ARG_ENABLE
  and AC_ARG_WITH arguments in one region, in the order defined.  The default
  behavior is to group options of each classes separately.

** AC_PROG_CC, AC_PROG_CXX
  No longer automatically arrange to declare the 'exit' function of C,
  when a C++ compiler is used.  Standard Autoconf macros no longer use
  'exit', so this is no longer an issue for them.  If you use C++, and
  want to call 'exit', you'll have to arrange for its declaration
  yourself.  But we now suggest you return from 'main' instead.

** AC_PROG_CC_C89, AC_PROG_CC_C99
  New macros for ISO C99 support.  AC_PROG_CC_C89 and AC_PROG_CC_C99
  check for ANSI C89 and ISO C99 support respectively.

** AC_PROG_CC_STDC
  Has been unobsoleted, and will check if the compiler supports ISO
  C99, falling back to ANSI C89 if not.  ac_cv_prog_cc_stdc is
  retained for backwards compatibility, assuming the value of
  ac_cv_prog_cc_c99 or ac_cv_prog_cc_c89 (whichever is valid, in
  that order).

** AC_STRUCT_DIRENT_D_INO, AC_STRUCT_DIRENT_D_TYPE
  New macros for checking commonly-used members of struct dirent.

** AC_SUBST
  The substituted value can now contain newlines.

** AC_SUBST_FILE
  The substitution now occurs only when @variable@ is on a line by itself,
  optionally surrounded by spaces and tabs.  The whole line is replaced.

** AC_TYPE_LONG_DOUBLE, AC_TYPE_LONG_DOUBLE_WIDER
  New macros to check for long double, and whether it is wider than double.
  The old macro AC_C_TYPE_LONG_DOUBLE has been marked as obsolete;
  applications should switch to the new macro.

** AC_TYPE_INT8_T, AC_TYPE_INT16_T, AC_TYPE_INT32_T, AC_TYPE_INT64_T,
   AC_TYPE_INTMAX_T, AC_TYPE_INTPTR_T, AC_TYPE_LONG_LONG_INT, AC_TYPE_SSIZE_T,
   AC_TYPE_UINT8_T, AC_TYPE_UINT16_T, AC_TYPE_UINT32_T, AC_TYPE_UINT64_T,
   AC_TYPE_UINTMAX_T, AC_TYPE_UINTPTR_T, AC_TYPE_UNSIGNED_LONG_LONG_INT
  New macros to check for C99 and POSIX types.

** AC_USE_SYSTEM_EXTENSIONS
  New macro to enable extensions to POSIX.

** AH_HEADER
  New macro which is defined to the name of the first declared config header
  or undefined if no config headers have been declared yet.

** AS_HELP_STRING
  The macro correctly handles quadrigraphs now.

** AS_BOURNE_COMPATIBLE, AS_SHELL_SANITIZE, AS_CASE
  These macros are new or published now.

** AT_COPYRIGHT
  New macro for copyright notices in testsuite files.

** ALLOCA, LIBOBJS, LTLIBOBJS
  Object names added to these variables are now prefixed with '${LIBOBJDIR}',
  as in '${LIBOBJDIR}alloca.o'.  LIBOBJDIR is meant to be defined from
  'Makefile.in' in case the object files lie in a different directory.
  The LIBOBJDIR feature is experimental.

** autoreconf
  Supports --no-recursive now.

** New macros to support Erlang/OTP.
  New macros for configuring paths to Erlang tools and libraries:
  AC_ERLANG_PATH_ERLC, AC_ERLANG_NEED_ERLC, AC_ERLANG_PATH_ERL,
  AC_ERLANG_NEED_ERL, AC_ERLANG_CHECK_LIB, AC_ERLANG_SUBST_ROOT_DIR,
  AC_ERLANG_SUBST_LIB_DIR.

  New macros for configuring installation of Erlang libraries:
  AC_ERLANG_SUBST_INSTALL_LIB_DIR, AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR.

** The manual now mentions Gnulib more prominently.

** New macros to support Objective C.
  AC_PROG_OBJC, AC_PROG_OBJCPP.

* Major changes in Autoconf 2.59b

  Released 2004-08-20, by Paul Eggert.

** AC_CHECK_ALIGNOF
  New macro that computes the default alignment of a type.

** AC_CHECK_TOOL, AC_PATH_TOOL, AC_CHECK_TOOLS
  When cross-compiling, these macros will give a warning if the tool
  is not prefixed.  In the future, unprefixed cross tools will not
  be detected; please consult the info documentation for information
  about the reason of this change.

** AC_CHECK_TARGET_TOOL, AC_PATH_TARGET_TOOL, AC_CHECK_TARGET_TOOLS
  New macros that detect programs whose name is prefixed with the
  target type, if the build type and target type are different.

** AC_REQUIRE_AUX_FILE
  New trace macro that declares expected auxiliary files.

** AC_PROG_GREP
  New macro that tests for a grep program that accepts as a long a line
  as possible.

** AC_PROG_EGREP, AC_PROG_FGREP
  These macros now require AC_PROG_GREP, and try EGREP="$GREP -E" and
  FGREP="$GREP -F" respectively if possible, or else run a path search for
  a program that accepts as long a line as possible.

** AC_PROG_SED
  New macro that tests for a sed program that truncates as few characters
  as possible.

* Major changes in Autoconf 2.59

  Released 2003-11-04, by Akim Demaille

** ac_abs_builddir etc.
  Absolute file names were actually relative in 2.58.

* Major changes in Autoconf 2.58

  Released 2003-11-04, by Akim Demaille

** core.*
  core.* files are no longer removed, as they may be valid user files.

** autoreconf and auxiliary directory
  Autoreconf creates the auxiliary directory if needed.  This is
  especially useful for initial "bootstrapping" of fresh CVS checkouts.

** AC_CONFIG_MACRO_DIR
  Use this macro to declare the directory for local M4 macros for aclocal.

** AC_LIBOBJS
  No longer includes twice the same file in LIBOBJS if invoked
  multiple times.

** AC_CONFIG_COMMANDS
  The directory for its first argument is automatically created.  For
  instance, with

      AC_CONFIG_COMMANDS([src/modules.hh], [...])

  $top_builddir/src/ is created if needed.

** Autotest and local.at
  The optional file local.at is always included in Autotest test suites.

** Warnings
  The warnings are always issued, including with cached runs.
  This became a significant problem since aclocal and automake can
  run autoconf behind the scene.

** autoheader warnings
  The warnings of autoheader can be turned off, using --warning.
  For instance, -Wno-obsolete disables the complaints about acconfig.h
  and other deprecated constructs.

** New macros
  AC_C_RESTRICT, AC_INCLUDES_DEFAULT, AC_LANG_ASSERT, AC_LANG_WERROR,
  AS_SET_CATFILE.

** AC_DECL_SYS_SIGLIST
  Works again.

** AC_FUNC_MKTIME
  Now checks that mktime is the inverse of localtime.

** Improve DJGPP portability
  The Autoconf tools and configure behave better under DJGPP.

** Present But Cannot Be Compiled
  New FAQ section dedicated to the mystic

    configure: WARNING: pi.h: present but cannot be compiled
    configure: WARNING: pi.h: check for missing prerequisite headers?
    configure: WARNING: pi.h: proceeding with the preprocessor's result
      messages.

** Concurrent executions of autom4te
  autom4te now locks its internal files, which enables concurrent
  executions of autom4te, likely to happen if automake, autoconf,
  autoheader etc. are run simultaneously.

** Libtool
  Use of Libtool 1.5 and higher is encouraged.  Compatibility with
  Libtool pre-1.4 is not checked.

** Autotest
  Testsuites no longer rerun failed tests in verbose mode; instead,
  failures are logged while the test is run.

  In addition, expected failures can be marked as such.

* Major changes in Autoconf 2.57

  Released 2002-12-03 by Paul Eggert.

Bug fixes for problems with AIX linker, with freestanding C compilers,
with GNU M4 limitations, and with obsolete copies of GNU documents.

The Free Documentation License has been upgraded from 1.1 to 1.2.

* Major changes in Autoconf 2.56

  Released 2002-11-15 by Akim Demaille.

One packaging problem fixed (config/install-sh was not executable).

* Major changes in Autoconf 2.55

  Released 2002-11-14 by Akim Demaille.

Release tips:

	   Have your configure.ac checked by autoscan ("autoscan").
	     Try the warning options ("autoreconf -fv -Wall").

** Documentation

- AC_CHECK_HEADER, AC_CHECK_HEADERS
  More information on proper use.

- Writing Test Programs

  This sections explains how to write good test sources to use with
  AC_COMPILE_IFELSE etc.  It documents AC_LANG_PROGRAM and so forth.

- AC_FOO_IFELSE vs. AC_TRY_FOO

  Explains why Autoconf moves from AC_TRY_COMPILE etc. to
  AC_COMPILE_IFELSE and AC_LANG_PROGRAM etc.

** autoreconf

- Is more robust to different Gettext installations.

- Produces messages (when --verbose) to be understood by Emacs'
  compile mode.

- Supports -W/--warnings.

- -m/--make
  Once the GNU Build System reinstalled, run './config.status
  --recheck && ./config.status && make' if possible.

** autom4te

- Supports --cache, and --no-cache.

- ~/.autom4te.cfg makes it possible to disable the caching mechanism
  (autom4te.cache).  See 'Customizing autom4te' in the documentation.

** config.status
  Supports --quiet.

** Obsolete options

  Support for the obsoleted options -m, --macrodir, -l, --localdir is
  dropped in favor of the safer --include/--prepend-include scheme.

** Macros

- New macros
  AC_COMPILER_IFELSE, AC_FUNC_MBRTOWC, AC_HEADER_STDBOOL,
  AC_LANG_CONFTEST, AC_LANG_SOURCE, AC_LANG_PROGRAM, AC_LANG_CALL,
  AC_LANG_FUNC_TRY_LINK, AC_MSG_FAILURE, AC_PREPROC_IFELSE.

- Obsoleted
  Obsoleted macros are kept for Autoconf backward compatibility, but
  should be avoided in configure.ac.  Running autoupdate is advised.
  AC_DECL_SYS_SIGLIST.

- AC_DEFINE/AC_DEFINE_UNQUOTED

  We have to stop using the old compatibility scheme --that tried to
  avoid useless backslashes-- because Libtool 1.4.3 contains a

  AC_DEFINE([error_t], [int],
	    [Define to a type to use for \`error_t' if it is not
	     otherwise available.])

  We have to quote the single quotes and backslashes with \.  The old
  compatibility scheme saw that ` was backslashed, and therefore did
  not quote the single quote...  Failure.  Hence, Autoconf 2.54 is not
  compatible with Libtool.  Autoconf 2.55 is, but in some cases might
  produce more \ than wanted.

  Please, note that in the future the same problem will happen with
  AC_MSG_*: use 'autoreconf -f -Wall'.

** Bug Fixes

- Portability of the Autoconf package to Solaris.

- Spurious warnings caused by config.status.
  This bug is benign, but painful: on some systems (typically
  FreeBSD), warnings such as:

     config.status: creating Makefile
     mv: Makefile: set owner/group (was: 1357/0): Operation not permitted

  could be issued.  This is fixed.

- Parallel Builds
  Simultaneous executions of config.status are possible again.

- Precious variables accumulation

  config.status could stack several copies of the precious variables
  assignments.


** Plans for later versions

- ./configure <host>

  The compatibility hooks with the old scheme will be completely
  removed.  Please, advice/use '--build', '--host', and '--target'
  only.

- AC_CHECK_HEADER, AC_CHECK_HEADERS

  The tests will be stricter, please make sure your invocations are
  valid.

- shell functions

  Shell functions will gradually be introduced, probably starting with
  Autotest.  If you know machines which are in use that you suspect
  *not* to support shell functions, please run the test suite of
  Autoconf 2.55 on it, and report the results to
  bug-autoconf@gnu.org.

- AC_MSG_*

  Special characters in AC_MSG_* need not be quoted.  Currently,
  Autoconf has heuristics to decide when a string is escaped, or has
  to be escaped.  This scheme is fragile, and will be removed; the
  only risk is uglified messages.  Please, run 'autoreconf -f -Wall'
  to find occurrences that will be affected.

* Major changes in Autoconf 2.54

  Released 2002-09-13 by Akim Demaille.

** Executables

- autoreconf no longer changes the version of the gettext/po/intl
  support files. It now adds the files the correspond to the
  AM_GNU_GETTEXT_VERSION declared in configure.ac.

  Warning: It now relies on the 'autopoint' program, which is part
  of GNU gettext 0.11.4 and newer.

  Please note that you need to have a GNU gettext version that
  corresponds at least to the AM_GNU_GETTEXT_VERSION declared
  in configure.ac. You can upgrade to newer GNU gettext versions,
  though, without needing to change configure.ac.

- The -I DIR or --include=DIR option now appends DIR to the include path
  instead of prepending; this is for consistency with other GNU tools.
  The new -B DIR or --prepend-include=DIR option has the old behavior.

** Macros

- AC_OUTPUT
  Now handles all the gory details about LIBOBJS and LTLIBOBJS.
  Please, remove lines such as

	# This is necessary so that .o files in LIBOBJS are also
	# built via the ANSI2KNR-filtering rules.
	LIBOBJS=`echo $LIBOBJS|sed 's/\.o /\$U.o /g;s/\.o$/\$U.o/'`

  and read the 'AC_LIBOBJ vs LIBOBJS' section.  Do not define U in
  your Makefiles either.

- AC_CONFIG_LINKS now makes copies if it can't make links.

- AC_FUNC_FNMATCH now tests only for POSIX compatibility, reverting to
  Autoconf 2.13 behavior.  The new macro AC_FUNC_FNMATCH_GNU also
  tests for GNU extensions to fnmatch, and replaces fnmatch if needed.

- AC_FUNC_SETVBUF_REVERSED no longer fails when cross-compiling.

- AC_PROG_CC_STDC is integrated into AC_PROG_CC.

- AC_PROG_F77 default search no longer includes cf77 and cfg77.

- New macros

  AC_C_BACKSLASH_A, AC_CONFIG_LIBOBJ_DIR, AC_GNU_SOURCE,
  AC_PROG_EGREP, AC_PROG_FGREP, AC_REPLACE_FNMATCH,
  AC_FUNC_FNMATCH_GNU, AC_FUNC_REALLOC, AC_TYPE_MBSTATE_T.

- AC_FUNC_GETLOADAVG
  looks for getloadavg.c in the CONFIG_LIBOBJ_DIR.

- AC_FUNC_MALLOC
  Now defines HAVE_MALLOC to 0 if 'malloc' does not work, and asks
  for an AC_LIBOBJ replacement.

** Bug fixes

- Spurious complaints from 'm4_bmatch' about invalid regular
  expressions are suppressed.

- Empty top_builddirs are properly handled.

- AC_CHECK_MEMBER works correctly when the member is an aggregate.

- AC_PATH_PROG
  Now colon in the optional path arguments are properly handled.

** Improved portability

- Both Autoconf the package, and the scripts it produces, should run
  more reliably with Zsh.  Bear in mind it is the default Bourne shell
  on Darwin.

- Autoconf and the scripts it produces no longer assume the existence of
  the obsolescent commands egrep and fgrep.

** Documentation

- Limitations of Make
  More of them.

- GNATS
  The GNATS base moved to
  https://bugs.gnu.org/cgi-bin/gnatsweb.pl?database=autoconf
  (It is no longer available, though.)

** Misc.

- config.log
  Now contains the list of output variables and files (AC_SUBST,
  AC_SUBST_FILES).

* Major changes in Autoconf 2.53

  Released 2002-03-08 by Akim Demaille.

** Requirements

  Perl 5.005_03 or later is required: autom4te is written in Perl and is
  needed by autoconf.  autoheader, autoreconf, ifnames, and autoscan are
  rewritten in Perl.

** Documentation

- AC_INIT
  Argument requirements, output variables, defined macros.
- M4sugar, M4sh, Autotest
  First sketch.
- Double quoting macros
  AC_TRY_CPP, AC_TRY_COMPILE, AC_TRY_LINK and AC_TRY_RUN.
- Licensing
  The Autoconf manual is now distributed under the terms of the GNU FDL.
- Section 'Hosts and Cross-Compilation'
  Explains the rationale for the 2.5x changes in the cross-compilation
  chain, and in the relationships between build, host, and target
  types.
  Emphasizes that 'cross-compilation' == '--host is given'.
  If you are working on compilers etc., be sure to read this section.
- Section 'AC_LIBOBJ vs. LIBOBJS'
  Explains why assigning LIBOBJS directly is now an error.
  Details how to update the code.

** configure

- $LINENO
  Now used instead of hard coded line numbers.
  This eases the comparison of 'configure's, and diminishes the
  pressure over control version archives.
  Automatic replacement for shells that don't support this feature.
- New output variables
  @builddir@, @top_builddir@, @abs_srcdir@, @abs_top_srcdir@, @abs_builddir@,
  @abs_top_builddir@.

** Emacs

  Autoconf and Autotest modes are provided.

** Executables

- autom4te
  New, used by the Autoconf suite to cache and speed up most processing.
- --force, -f
  Supported by autom4te, autoconf and autoheader.
- --include, -I
  Replaces --autoconf-dir and --localdir in autoconf, autoheader,
  autoupdate, and autoreconf.
- autoreconf
  No longer passes --cygnus, --foreign, --gnits, --gnu, --include-deps:
  automake options are to be given via AUTOMAKE_OPTIONS.
- autoreconf
  Runs gettextize and libtoolize when appropriate.
- autoreconf
  --m4dir is no longer supported.
- autoreconf
  Now runs only in the specified directories, defaulting to '.',
  but understands AC_CONFIG_SUBDIRS for dependent directories.
  Before, it used to run on all the 'configure.ac' found in the
  current tree.
  Independent packages are properly updated.

** Bug fixes

- The top level $prefix is propagated to the AC_CONFIG_SUBDIRS configures.
- AC_TRY_RUN
  Under the user pressure, $? is finally available.  Probably a mistake.
- AC_F77_LIBRARY_LDFLAGS now supports the HP-UX f90 compiler.
- Precious variables accumulation
  config.status could stack several copies of the precious variables
  assignments.
- AC_PATH_PROG and family.
  Works properly when given a literal path.
- AC_FUNC_SETPGRP
  Somewhere since 2.13, the result had been reversed.

** C Macros

- AC_C_BIGENDIAN supports the cross-compiling case.
- AC_C_BIGENDIAN accepts ACTION-IF-TRUE, ACTION-IF-FALSE, and
  ACTION-IF-UNKNOWN arguments.  All are optional, and the default
  for ACTION-IF-TRUE is to define WORDS_BIGENDIAN like AC_C_BIGENDIAN
  always did.
- AC_C_LONG_DOUBLE now succeeds only if 'long double' has more range or
  precision than 'double'.

** Generic macros

- AC_INIT
  It now defines the preprocessor symbols PACKAGE_NAME,
  PACKAGE_TARNAME, PACKAGE_VERSION, PACKAGE_STRING, and
  PACKAGE_BUGREPORT.

- AC_INIT
  Admits a fourth optional parameter: the tar name.

- AC_CONFIG_COMMANDS, HEADERS, FILES, LINKS.
  Provide the user with srcdir, ac_srcdir, ac_top_srcdir, ac_builddir,
  ac_top_builddir, ac_abs_srcdir, ac_abs_top_srcdir, ac_abs_builddir,
  ac_abs_top_builddir.

- AC_CONFIG_COMMANDS, HEADERS, FILES, LINKS and AC_OUTPUT.
  Are much less expensive when using long lists of files.

- AC_PREFIX_PROGRAM
  Works with shell variables, and non alphanumeric names.

** Library macros

- AC_FUNC_STRERROR_R now sets STRERROR_R_CHAR_P, not HAVE_WORKING_STRERROR_R,
  because POSIX 1003.1-200x draft 7 says strerror_r returns int, not char *.

- AC_FUNC_STRTOD substitutes POW_LIB.

- AC_FUNC_STRNLEN
  New.

* Major changes in Autoconf 2.52

  Released 2001-07-18 by Akim Demaille.

** Documentation
- AC_ARG_VAR
- Quadrigraphs
  This feature was present in autoconf 2.50 but was not documented.
  For example, '@<:@' is translated to '[' just before output.  This
  is useful when writing strings that contain unbalanced quotes, or
  other hard-to-quote constructs.
- m4_pattern_forbid, m4_pattern_allow
- Tips for upgrading from 2.13.
- Using autoscan to maintain a configure.ac.

** Default includes
- Now include stdint.h.
- sys/types.h and sys/stat.h are guarded.
- strings.h is included if available, and not conflicting with string.h.

** Bug fixes
- The test suite is more robust and presents less false failures.
- Invocation of GNU M4 now robust to POSIXLY_CORRECT.
- configure accepts --prefix='' again.
- AC_CHECK_LIB works properly when its first argument is not a
  literal.
- HAVE_INTTYPES_H is defined only if not conflicting with sys/types.h.
- build_, host_, and target_alias are AC_SUBST as in 2.13.
- AC_ARG_VAR properly propagates precious variables inherited from the
  environment to ./config.status.
- Using --program-suffix/--program-prefix is portable.
- Failures to detect the default compiler's output extension are less
  likely.
- 'config.status foo' works properly when 'foo' depends on variables
  set in an AC_CONFIG_THING INIT-CMD.
- autoheader is more robust to broken input.
- Fixed Fortran name-mangling and link tests on a number of systems,
  e.g. NetBSD; see AC_F77_DUMMY_MAIN, below.

** Generic macros
- AC_CHECK_HEADER and AC_CHECK_HEADERS support a fourth argument to
  specify pre-includes.  In this case, the headers are compiled with
  cc, not merely preprocessed by cpp.  Therefore it is the _usability_
  of a header which is checked for, not just its availability.
- AC_ARG_VAR refuses to run configure when precious variables have
  changed.
- Versions of compilers are dumped in the logs.
- AC_CHECK_TYPE recognizes use of 'foo_t' as a replacement type.

** Specific Macros
- AC_PATH_XTRA only adds -ldnet to $LIBS if it's needed to link.
- AC_FUNC_WAIT3 and AC_SYS_RESTARTABLE_SYSCALLS are obsoleted.
- AM_FUNC_ERROR_AT_LINE, AM_FUNC_FNMATCH, AM_FUNC_MKTIME,
  AM_FUNC_OBSTACK, and AM_FUNC_STRTOD are now activated.
  Be sure to read 'Upgrading from Version 2.13' to understand why
  running 'autoupdate' is needed.
- AC_F77_DUMMY_MAIN, AC_F77_MAIN: new macros to detect whether
  a main-like routine is required/possible when linking C/C++ with
  Fortran.  Users of e.g. AC_F77_WRAPPERS should be aware of these.
- AC_FUNC_GETPGRP behaves better when cross-compiling.

* Major changes in Autoconf 2.51
There was no release of Autoconf 2.51 since some packagers had used
this version number without permission to ship intermediary versions
of 2.50.  The version was skipped to avoid confusion.

* Major changes in Autoconf 2.50

  Released 2001-05-21 by Akim Demaille.

** Lots of bug fixes
There have been far too many to enumerate them here.  Check out
ChangeLog if you really want to know more.

** Improved documentation
In particular, portability issues are better covered.

** Use of Automake
All the standard GNU Makefile targets are supported.  The layout has
changed: m4/ holds the M4 extensions Autoconf needs for its
configuration, doc/ contains the documentation, and tests/ contains
the test suite.

** Man pages are provided
For autoconf, autoreconf, autoupdate, autoheader, autoscan, ifnames,
config.guess, config.sub.

** autoconf
- --trace
  Provides a safe and powerful means to trace the macro uses.  This
  provide the parsing layer for tools which need to 'study'
  configure.in.

- --warnings
  Specify what category of warnings should be enabled.

- When recursing into subdirectories, try for configure.gnu before
  configure to adapt for packages not using autoconf on case-insensitive
  file systems.

- Diagnostics
  More errors are now caught (circular AC_REQUIRE dependencies,
  AC_DEFINE in the action part of an AC_CACHE_CHECK, too many pops
  etc.).  In addition, their location and call stack are given.

** autoupdate
autoupdate is much more powerful, and is able to provide the glue code
which might be needed to move from an old macro to its newer
equivalent.

You are strongly encouraged to use it to modernize both your
'configure.in' and your .m4 extension files.

** autoheader
The internal machinery of autoheader has completely changed.  As a
result, using 'acconfig.h' should be considered to be obsoleted, and
you are encouraged to get rid of it using the AH macros.

** autoreconf
Extensive overhaul.

** Fortran 77 compilers
Globally, the support for Fortran 77 is considerably improved.

Support for automatically determining a Fortran 77 compiler's
name-mangling scheme.  New CPP macros F77_FUNC and F77_FUNC_ are
provided to wrap C/C++ identifiers, thus making it easier and more
transparent for C/C++ to call Fortran 77 routines, and Fortran 77 to
call C/C++ routines.  See the Texinfo documentation for details.

** Test suite
The test suite no longer uses DejaGNU.  It should be easy to submit
test cases in this new framework.

** configure
- --help, --help=long, -hl
  no longer dumps useless items.
- --help=short, -hs
  lists only specific options.
- --help=recursive, -hr
  displays the help of all the embedded packages.
- Remembers environment variables when reconfiguring.
  The previous scheme to set envvar before running configure was
    ENV=VAL ./configure
  what prevented configure from remembering the environment in which
  it was run, therefore --recheck was run in an inconsistent
  environment.  Now, one should run
    ./configure ENV=VAR
  and then --recheck will work properly.  Variables declared with
  AC_ARG_VAR are also preserved.
- cross-compilation
  $build defaults to `config.guess`, $host to $build, and then $target
  to $host.
  Cross-compilation is a global status of the package, it no longer
  depends upon the current language.
  Cross compilation is enabled iff the user specified '--host'.
  'configure' now fails if it can't run the executables it compiles,
  unless cross-compilation is enabled.
- Cache file
  The cache file is disabled by default.  The new options
  '--config-cache', '-C' set the cache to 'config.cache'.

** config.status
- faster
  Much faster on most architectures.
- concurrent executions
  It is safe to use 'make -j' with config.status.
- human interface improved
  It is possible to invoke
    ./config.status foobar
  instead of the former form (still valid)
    CONFIG_COMMANDS= CONFIG_HEADERS= CONFIG_LINKS= \
    CONFIG_FILES=foobar:foo.in:bar.in \
    ./config.status
  The same holds for configuration headers and links.
  You can instantiate unknown files and headers:
    ./config.status --header foo.h:foo.h.in --file bar:baz
- has a useful --help
- accepts special file name "-" for stdin/stdout


** Identity Macros
- AC_COPYRIGHT
  Specify additional copyright information.

- AC_INIT
  Now expects the identity of the package as argument.

** General changes.
- Uniform quotation
  Most macros, if not all, now strictly follow the 'one quotation
  level' rule.  This results in a more predictable expansion.

- AC_REQUIRE
  A sly bug in the AC_REQUIRE machinery, which could produce incorrect
  configure scripts, was fixed by Axel Thimm.

** Setup Macros
- AC_ARG_VAR
  Document and ask for the registration of an envvar.

- AC_CONFIG_SRCDIR
  Specifies the file which 'configure' should look for when trying to
  find the source tree (used to be handled by AC_INIT).

- AC_CONFIG_COMMANDS
  To add new actions to config.status.  Should be used instead of
  AC_OUTPUT_COMMANDS.

- AC_CONFIG_LINKS
  Replaces AC_LINK_FILES.

- AC_CONFIG_HEADERS, AC_CONFIG_COMMANDS, AC_CONFIG_SUBDIRS,
  AC_CONFIG_LINKS, and AC_CONFIG_FILES
  They now obey sh: you should no longer use shell variables as
  argument.  Instead of

	test "$package_foo_enabled" = yes && $my_subdirs="$my_subdirs foo"
	AC_CONFIG_SUBDIRS($my_subdirs)

  write

	if test "$package_foo_enabled" = yes; then
	  AC_CONFIG_SUBDIRS(foo)
	fi

- AC_HELP_STRING
  To format an Autoconf macro's help string so that it looks pretty
  when the user executes 'configure --help'.


** Generic Test Macros
- AC_CHECK families
  The interface of the AC_CHECK families of macros (decl, header,
  type, member, func) is now uniform.  They support the same set of
  default includes.

- AC_CHECK_DECL, AC_CHECK_DECLS
  To check whether a symbol is declared.

- AC_CHECK_SIZEOF, AC_C_CHAR_UNSIGNED.
  No longer need a cross-compilation default.

- AC_CHECK_TYPE
  The test it performs is much more robust than previously, and makes
  it possible to test builtin types in addition to typedefs.
  It is now schizophrenic:
    - AC_CHECK_TYPE(TYPE, REPLACEMENT)
      remains for backward compatibility, but its use is discouraged.
    - AC_CHECK_TYPE(TYPE, IF-FOUND, IF-NOT-FOUND, INCLUDES)
      behaves exactly like the other AC_CHECK macros.

- AC_CHECK_TYPES
  Checks whether given types are supported by the system.

- AC_CHECK_MEMBER, AC_CHECK_MEMBERS
  Check for given members in aggregates (e.g., pw_gecos in struct
  passwd).

- AC_PROG_CC_STDC
  Checks if the compiler supports ISO C, included when needs special
  options.

- AC_PROG_CPP
  Checking whether the preprocessor indicates missing includes by the
  error code. stderr is checked by AC_TRY_CPP only as a fallback.

- AC_LANG
  Takes a language as argument and replaces AC_LANG_C,
  AC_LANG_CPLUSPLUS and AC_LANG_FORTRAN77.

- AC_LANG_PUSH, AC_LANG_POP
  Are preferred to AC_LANG_SAVE, AC_LANG_RESTORE.

** Specific Macros
- AC_FUNC_CHOWN, AC_FUNC_MALLOC, AC_FUNC_STRERROR_R,
  AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK, AC_FUNC_STAT, AC_FUNC_LSTAT,
  AC_FUNC_ERROR_AT_LINE, AC_FUNC_OBSTACK, AC_FUNC_STRTOD, AC_FUNC_FSEEKO.
  New.

- AC_FUNC_GETGROUPS
  Sets GETGROUPS_LIBS.

- AC_FUNC_GETLOADAVG
  Defines 'HAVE_STRUCT_NLIST_N_UN_N_NAME' instead of 'NLIST_NAME_UNION'.

- AC_PROG_LEX
  Now integrates 'AC_DECL_YYTEXT' which is obsoleted.

- AC_SYS_LARGEFILE
  Arrange for large-file support.

- AC_EXEEXT, AC_OBJEXT
  You are no longer expected to use them: their computation is
  performed by default.

** C++ compatibility
  Every macro has been revisited in order to support at best CC=c++.

Major changes in Autoconf 2.14:
  There was no release of GNU Autoconf 2.14.

Major changes in Autoconf 2.13:

  Released 1999-05-01 by Ben Elliston.

* Support for building on 32-bit Windows systems where the only available C or
  C++ compiler is the Microsoft Visual C++ command line compiler
  ('cl').  Additional support for building on 32-bit Windows systems which are
  using the Cygwin or Mingw32 environments.
* Support for alternative object file and executable file extensions.
  On 32-bit Windows, for example, these are .obj and .exe. These are discovered
  using AC_OBJEXT and AC_EXEEXT, which substitute @OBJEXT@ and
  @EXEEXT@ in the output, respectively.
* New macros: AC_CACHE_LOAD, AC_CACHE_SAVE, AC_FUNC_SELECT_ARGTYPES,
  AC_VALIDATE_CACHED_SYSTEM_TUPLE, AC_SEARCH_LIBS, AC_TRY_LINK_FUNC,
  AC_C_STRINGIZE, AC_CHECK_FILE(S), AC_PROG_F77 (and friends).
* AC_DEFINE now has an optional third argument for a description to be
  placed in the config header input file (e.g. config.h.in).
* The C++ code fragment compiled for the C++ compiler test had to be
  improved to include an explicit return type for main(). This was
  causing failures on systems using recent versions of the EGCS C++
  compiler.
* Fixed an important bug in AC_CHECK_TYPE that would cause a configure
  script to report that 'sometype_t' was present when only 'type_t'
  was defined.
* Merge of the FSF version of config.guess and config.sub to modernize
  these scripts. Add support for a few new hosts in config.guess.
  Incorporate latest versions of install-sh, mkinstalldirs and
  texinfo.tex from the FSF.
* autoreconf is capable of running automake if necessary (and
  applicable).
* Support for Fortran 77. See the Texinfo documentation for details.
* Bug fixes and workarounds for quirky bugs in vendor utilities.

Major changes in Autoconf 2.12:

  Released 1996-11-26 by David J. MacKenzie

* AC_OUTPUT and AC_CONFIG_HEADERS can create output files by
  concatenating multiple input files separated by colons, like so:
  AC_CONFIG_HEADERS([config.h:conf.pre:config.h.in:conf.post])
  AC_OUTPUT([Makefile:Makefile.in:Makefile.rules])
  The arguments may be shell variables, to compute the lists on the fly.
* AC_LINK_FILES and AC_CONFIG_SUBDIRS may be called multiple times.
* New macro AC_OUTPUT_COMMANDS adds more commands to run in config.status.
* Bug fixes.

Major changes in Autoconf 2.11:

  Released November 18th, 1996, by David J. MacKenzie

* AC_PROG_CC and AC_PROG_CXX check whether the compiler works.
  They also default CFLAGS/CXXFLAGS to "-g -O2" for gcc, instead of "-g -O".
* AC_REPLACE_FUNCS defines HAVE_foo if the system has the function 'foo'.
* AC_CONFIG_HEADERS expands shell variables in its argument.
* New macros: AC_FUNC_FNMATCH, AC_FUNC_SETPGRP.
* The "checking..." messages and the source code for test programs that
  fail are saved in config.log.
* Another workaround has been added for seds with small command length limits.
* config.sub and config.guess recognize more system types.
* Bug fixes.

Major changes in Autoconf 2.10:

  Released May 7th, 1996, by Roland McGrath

* Bug fixes.
* The cache variable names used by 'AC_CHECK_LIB(LIB, FUNC, ...)' has
  changed: now $ac_cv_lib_LIB_FUNC, previously $ac_cv_lib_LIB.

Major changes in Autoconf 2.9:

  Released March 16th, 1996, by Roland McGrath

* Bug fixes.

Major changes in Autoconf 2.8:

  Released March 8th, 1996, by Roland McGrath

* Bug fixes.

Major changes in Autoconf 2.7:

  Released November 22nd, 1995, by David J. MacKenzie

* Bug fixes.

Major changes in Autoconf 2.6:

  Released November 20th, 1995, by David J. MacKenzie

* Bug fixes.

Major changes in Autoconf 2.5:

  Released November 17th, 1995, by Roland McGrath

* New configure options --bindir, --libdir, --datadir, etc., with
  corresponding output variables.
* New macro: AC_CACHE_CHECK, to make using the cache easier.
* config.log contains the command being run as well as any output from it.
* AC_CHECK_LIB can check for libraries with "." or "/" or "+" in their name.
* AC_PROG_INSTALL doesn't cache a name for install-sh, for sharing caches.
* AC_CHECK_PROG, AC_PATH_PROG, AC_CHECK_PROGS, AC_PATH_PROGS, and
  AC_CHECK_TOOL can search a path other than $PATH.
* AC_CHECK_SIZEOF takes an optional size to use when cross-compiling.

Major changes in Autoconf 2.4:

  Released June 14th, 1995, by David J. MacKenzie

* Fix a few bugs found by Emacs testers.

Major changes in Autoconf 2.3:

  Released March 27th, 1995, by David J. MacKenzie

* Fix the cleanup trap in several ways.
* Handle C compilers that are picky about option placement.
* ifnames gets the version number from the right directory.

Major changes in Autoconf 2.2:

  Released March 8th, 1995, by David J. MacKenzie

* The ifnames utility is much faster but requires a "new awk" interpreter.
* AC_CHECK_LIB and AC_HAVE_LIBRARY check and add the new
  library before existing libs, not after, in case it uses them.
* New macros: AC_FUNC_GETPGRP, AC_CHECK_TOOL.
* Lots of bug fixes.
* Many additions to the TODO file :-)

Major changes in Autoconf 2.1:

  Released November 4th, 1994, by David J. MacKenzie

* Fix C++ problems.
* More explanations in the manual.
* Fix a spurious failure in the testsuite.
* Clarify some warning messages.
* autoreconf by default only rebuilds configure and config.h.in files
  that are older than any of their particular input files; there is a
  --force option to use after installing a new version of Autoconf.

Thanks to everybody who's submitted changes and additions to Autoconf!
I've incorporated many of them, and am still considering others for
future releases -- but I didn't want to postpone this release indefinitely.

Caution: don't indiscriminately rebuild configure scripts with
Autoconf version 2.  Some configure.in files need minor adjustments to
work with it; the documentation has a chapter on upgrading.  A few
configure.in files, including those for GNU Emacs and the GNU C
Library, need major changes because they relied on undocumented
internals of version 1.  Future releases of those packages will have
updated configure.in files.

It's best to use GNU M4 1.3 (or later) with Autoconf version 2.
Autoconf now makes heavy use of M4 diversions, which were implemented
inefficiently in GNU M4 releases before 1.3.

Major changes in Autoconf 2.0:

  Released October 26th, 1994, by David J. MacKenzie

** New copyright terms:
* There are no restrictions on distribution or use of configure scripts.

** Documentation:
* Autoconf manual is reorganized to make information easier to find
  and has several new indexes.
* INSTALL is reorganized and clearer and is now made from Texinfo source.

** New utilities:
* autoscan to generate a preliminary configure.in for a package by
  scanning its source code for commonly used nonportable functions,
  programs, and header files.
* ifnames to list the symbols used in #if and #ifdef directives in a
  source tree.
* autoupdate to update a configure.in to use the version 2 macro names.
* autoreconf to recursively remake configure and configuration header
  files in a source tree.

** Changed utilities:
* autoheader can take pieces of acconfig.h to replace config.h.{top,bot}.
* autoconf and autoheader can look for package-local definition files
  in an alternate directory.

** New macros:
* AC_CACHE_VAL to share results of tests between configure runs.
* AC_DEFUN to define macros, automatically AC_PROVIDE them, and ensure
  that macros invoked with AC_REQUIRE don't interrupt other macros.
* AC_CONFIG_AUX_DIR, AC_CANONICAL_SYSTEM, AC_CANONICAL_HOST, AC_LINK_FILES to
  support deciding unguessable features based on the host and target types.
* AC_CONFIG_SUBDIRS to recursively configure a source tree.
* AC_ARG_PROGRAM to use the options --program-prefix,
  --program-suffix, and --program-transform-name to change the names
  of programs being installed.
* AC_PREFIX_DEFAULT to change the default installation prefix.
* AC_TRY_COMPILE to compile a test program without linking it.
* AC_CHECK_TYPE to check whether sys/types.h or stdlib.h defines a given type.
* AC_CHECK_LIB to check for a particular function and library.
* AC_MSG_CHECKING and AC_MSG_RESULT to print test results, on a single line,
  whether or not the test succeeds.  They obsolete AC_CHECKING and AC_VERBOSE.
* AC_SUBST_FILE to insert one file into another.
* AC_FUNC_MEMCMP to check whether memcmp is 8-bit clean.
* AC_FUNC_STRFTIME to find strftime even if it's in -lintl.
* AC_FUNC_GETMNTENT to find getmntent even if it's in -lsun or -lseq.
* AC_HEADER_SYS_WAIT to check whether sys/wait.h is POSIX.1 compatible.

** Changed macros:
* Many macros renamed systematically, but old names are accepted for
  backward compatibility.
* AC_OUTPUT adds the "automatically generated" comment to
  non-Makefiles where it finds @configure_input@ in an input file, to
  support files with various comment syntaxes.
* AC_OUTPUT does not replace "prefix" and "exec_prefix" in generated
  files when they are not enclosed in @ signs.
* AC_OUTPUT allows the optional environment variable CONFIG_STATUS to
  override the file name "config.status".
* AC_OUTPUT takes an optional argument for passing variables from
  configure to config.status.
* AC_OUTPUT and AC_CONFIG_HEADERS allow you to override the input-file names.
* AC_OUTPUT automatically substitutes the values of CFLAGS, CXXFLAGS,
  CPPFLAGS, and LDFLAGS from the environment.
* AC_PROG_CC and AC_PROG_CXX now set CFLAGS and CXXFLAGS, respectively.
* AC_PROG_INSTALL looks for install-sh or install.sh in the directory
  specified by AC_CONFIG_AUXDIR, or srcdir or srcdir/.. or
  srcdir/../.. by default.
* AC_DEFINE, AC_DEFINE_UNQUOTED, and AC_SUBST are more robust and smaller.
* AC_DEFINE no longer prints anything, because of the new result reporting
  mechanism (AC_MSG_CHECKING and AC_MSG_RESULT).
* AC_VERBOSE pays attention to --quiet/--silent, not --verbose.
* AC_ARG_ENABLE and AC_ARG_WITH support whitespace in the arguments to
  --enable- and --with- options.
* AC_CHECK_FUNCS and AC_CHECK_HEADERS take optional shell commands to
  execute on success or failure.
* Checking for C functions in C++ works.

** Removed macros:
* AC_REMOTE_TAPE and AC_RSH removed; too specific to tar and cpio, and
  better maintained with them.
* AC_ARG_ARRAY removed because no one was likely using it.
* AC_HAVE_POUNDBANG replaced with AC_SYS_INTERPRETER, which doesn't
  take arguments, for consistency with all of the other specific checks.

** New files:
* Comes with config.sub and config.guess, and uses them optionally.
* Uses config.cache to cache test results.  An alternate cache file
  can be selected with the --cache-file=FILE option.
* Uses optional shell scripts $prefix/share/config.site and
  $prefix/etc/config.site to perform site or system specific initializations.
* configure saves compiler output to ./config.log for debugging.
* New files autoconf.m4 and autoheader.m4 load the other Autoconf macros.
* acsite.m4 is the new name for the system-wide aclocal.m4.
* Has a DejaGnu test suite.

Major changes in Autoconf 1.11:

* AC_PROG_INSTALL calls install.sh with the -c option.
* AC_SET_MAKE cleans up after itself.
* AC_OUTPUT sets prefix and exec_prefix if they weren't set already.
* AC_OUTPUT prevents shells from looking in PATH for config.status.

Plus a few other bug fixes.

Major changes in Autoconf 1.10:

* autoheader uses config.h.bot if present, analogous to config.h.top.
* AC_PROG_INSTALL looks for install.sh in srcdir or srcdir/.. and
  never uses cp.
* AC_PROG_CXX looks for cxx as a C++ compiler.

Plus several bugs fixed.

Major changes in Autoconf 1.9:

* AC_YYTEXT_POINTER replaces AC_DECLARE_YYTEXT.
* AC_SIZEOF_TYPE generates the cpp symbol name automatically,
  and autoheader generates entries for those names automatically.
* AC_FIND_X gets the result from xmkmf correctly.
* AC_FIND_X assumes no X if --without-x was given.
* AC_FIND_XTRA adds libraries to the variable X_EXTRA_LIBS.
* AC_PROG_INSTALL finds OSF/1 installbsd.

Major changes in Autoconf 1.8:

** New macros:
* New macros AC_LANG_C, AC_LANG_CPLUSPLUS, AC_LANG_SAVE, AC_LANG_RESTORE,
  AC_PROG_CXX, AC_PROG_CXXCPP, AC_REQUIRE_CPP
  for checking both C++ and C features in one configure script.
* New macros AC_CHECKING, AC_VERBOSE, AC_WARN, AC_ERROR for printing messages.
* New macros AC_FIND_XTRA, AC_MMAP, AC_SIZEOF_TYPE, AC_PREREQ,
  AC_SET_MAKE, AC_ENABLE.

** Changed macros:
* AC_FIND_X looks for X in more places.
* AC_PROG_INSTALL defaults to install.sh instead of cp, if it's in srcdir.
  install.sh is distributed with Autoconf.
* AC_DECLARE_YYTEXT has been removed because it can't work, pending
  a rewrite of quoting in AC_DEFINE.
* AC_OUTPUT adds its comments in C format when substituting in C files.
* AC_COMPILE_CHECK protects its ECHO-TEXT argument with double quotes.

** New or changed command line options:
* configure accepts --enable-FEATURE[=ARG] and --disable-FEATURE options.
* configure accepts --without-PACKAGE, which sets withval=no.
* configure accepts --x-includes=DIR and --x-libraries=DIR.
* Giving --with-PACKAGE no argument sets withval=yes instead of withval=1.
* configure accepts --help, --version, --silent/--quiet, --no-create options.
* configure accepts and ignores most other Cygnus configure options, and
  warns about unknown options.
* config.status accepts --help, --version options.

** File names and other changes:
* Relative srcdir values are not made absolute.
* The values of @prefix@ and @exec_prefix@ and @top_srcdir@ get substituted.
* Autoconf library files are installed in ${datadir}/autoconf, not ${datadir}.
* autoheader optionally copies config.h.top to the beginning of config.h.in.
* The example Makefile dependencies for configure et al. work better.
* Namespace cleanup: all shell variables used internally by Autoconf
  have names beginning with 'ac_'.

More big improvements are in process for future releases, but have not
yet been (variously) finished, integrated, tested, or documented enough
to release yet.

Major changes in Autoconf 1.7:

* New macro AC_OBSOLETE.
* Bugs in Makefile.in fixed.
* AC_LONG_FILE_NAMES improved.

Major changes in Autoconf 1.6:

* New macro AC_LONG_64_BITS.
* Multiple .h files can be created.
* AC_FIND_X looks for X files directly if it doesn't find xmkmf.
* AC_ALLOCA defines C_ALLOCA if using alloca.c.
* --with-NAME can take a value, e.g., --with-targets=sun4,hp300bsd.
* Unused --no-create option to configure removed.
* autoheader doesn't change the timestamp of its output file if
  the file didn't change.
* All macros that look for libraries now use AC_HAVE_LIBRARY.
* config.status checks three optional environment variables to
  modify its behavior.
* The usual bug fixes.

Major changes in Autoconf 1.5:

* New macros AC_FIND_X, AC_OFF_T, AC_STAT_MACROS_BROKEN, AC_REVISION.
* autoconf and autoheader scripts have GNU standards conforming
  --version and --help options (they print their message and exit).
* Many bug fixes.

Major changes in Autoconf 1.4:

* New macros AC_HAVE_POUNDBANG, AC_TIME_WITH_SYS_TIME, AC_LONG_DOUBLE,
  AC_GETGROUPS_T, AC_DEFINE_UNQUOTED.
* autoconf and autoheader use the M4 environment variable to determine the
  name of the M4 program to use.
* The --macrodir option to autoconf and autoheader specifies the directory
  in which acspecific.m4, acgeneral.m4, etc. reside if not the default.
* autoconf and autoheader can take '-' as their file names, which means to
  read stdin as input.
* Resulting configure scripts can take a --verbose option which causes them
  to print the results of their tests.
* AC_DEFINE quotes its second argument in such a way that spaces, magic
  shell characters, etc. will be preserved during various stages of
  expansion done by the shell.  If you don't want this, use
  AC_DEFINE_UNQUOTED instead.
* Much textual processing done with external calls to tr and sed have been
  internalized with builtin M4 'patsubst' and 'translit' calls.
* AC_OUTPUT doesn't hardwire the file names it outputs.  Instead, you can
  set the shell variables 'gen_files' and 'gen_config' to the list of
  file names to output.
* AC_DECLARE_YYTEXT does an AC_SUBST of 'LEX_OUTPUT_ROOT', which may be
  "lex.yy" or "lexyy", depending on the system.
* AC_PROGRAMS_CHECK takes an optional third arg.  If given, it is used as
  the default value.
* If AC_ALLOCA chooses alloca.c, it also defines STACK_DIRECTION.
* AC_CONST works much more reliably on more systems.
* Many bug fixes.

Major changes in Autoconf 1.3:

configure no longer requires awk for packages that use a config.h.
Support handling --with-PACKAGE options.
New 'autoheader' script to create 'config.h.in' from 'configure.in'.
Ignore troublesome -lucb and -lPW when searching for alloca.
Rename --exec_prefix to --exec-prefix for GNU standards conformance.
Improve detection of STDC library.
Add AC_HAVE_LIBRARY to check for non-default libraries.
Function checking should work with future GNU libc releases.

Major changes in Autoconf 1.2:

The --srcdir option is now usually unnecessary.
Add a file containing sample comments describing CPP macros.
A comment in config.status tells which host it was configured on.
Substituted variable values can now contain commas.
Fix bugs in various feature checks.

Major changes in Autoconf 1.1:

Added AC_STRCOLL macro.
Made AC_GETLOADAVG check for more things.
AC_OUTPUT argument is now optional.
Various bug fixes.

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