Use compatibility regex library also on AIX

This augments 3632cfc (Use compatibility regex library on Darwin,
2008-09-07), which already carries a "Tested-by" statement for AIX,
but that test was actually done with this patch included.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Tested-by: Mike Ralphson <mike@abacus.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -702,6 +702,8 @@ ifeq ($(uname_S),AIX)
 	INTERNAL_QSORT = UnfortunatelyYes
 	NEEDS_LIBICONV=YesPlease
 	BASIC_CFLAGS += -D_LARGE_FILES
+	COMPAT_CFLAGS += -Icompat/regex
+	COMPAT_OBJS += compat/regex/regex.o
 endif
 ifeq ($(uname_S),GNU)
 	# GNU/Hurd