Use quotes for config.h to handle experimental build.mk

src/compat/memmem.c

@@ -29,7 +29,9 @@
 #include <sys/types.h>
 /* $FreeBSD: head/lib/libc/string/memmem.c 188080 2009-02-03 17:58:20Z danger $ */
 #include <string.h>
-#include <config.h>
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
 
 #ifndef HAVE_MEMMEM
 /*