Index: external/bsd/byacc/bin/Makefile
===================================================================
RCS file: /cvsroot/src/external/bsd/byacc/bin/Makefile,v
retrieving revision 1.6
diff -p -u -r1.6 Makefile
--- external/bsd/byacc/bin/Makefile	14 Apr 2015 14:08:36 -0000	1.6
+++ external/bsd/byacc/bin/Makefile	1 May 2015 20:08:27 -0000
@@ -13,3 +13,8 @@ COPTS.output.c += -Wno-format-nonliteral
 COPTS.reader.c += -Wno-format-nonliteral
 
 .include <bsd.prog.mk>
+
+DPSRCS+=	CPPFLAGS
+CPPFLAGS: rebuild
+	echo '#' ${CPPFLAGS} > $@.tmp && cmp $@.tmp $@ || mv -f $@.tmp $@
+rebuild: .PHONY