compat/regex: get the gawk regex engine to compile within git

We need to define -DGAWK -DNO_MBSUPPORT so that the gawk regex engine
will compile, and include stdio.h and stddef.h in regex.h. Gawk itself
includes these headers before it includes the regex.h header.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1878,6 +1878,10 @@ ifdef NO_EXPAT
 http-walker.s http-walker.o: EXTRA_CPPFLAGS = -DNO_EXPAT
 endif
 
+ifdef NO_REGEX
+compat/regex/regex.o: EXTRA_CPPFLAGS = -DGAWK -DNO_MBSUPPORT
+endif
+
 git-%$X: %.o $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(LIBS)
 

compat/regex/regex.h

@@ -1,3 +1,6 @@
+#include <stdio.h>
+#include <stddef.h>
+
 /* Definitions for data structures and routines for the regular
    expression library.
    Copyright (C) 1985,1989-93,1995-98,2000,2001,2002,2003,2005,2006,2008