Fix compilation with GNU Make 3.82 (patch from Nixpkgs).

diff --git a/Makefile b/Makefile
index 09fb3ed..59eba16 100644
--- a/Makefile
+++ b/Makefile
@@ -174,7 +174,7 @@ INSTALL := $(BINFILES) $(MANFILES)
 # want this rule first, use := on ALL, and ALL not filled in yet
 all: do_all
 
--include */module.mk
+-include proc/module.mk ps/module.mk
 
 do_all:    $(ALL)
