fmap: request libc compatibility level that includes memccpy

Change-Id: I928efe6f63305a0099d64e83091aa80768582f48
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/10160
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

util/cbfstool/flashmap/fmap.c

@@ -32,6 +32,8 @@
  * Software Foundation.
  */
 
+#define _XOPEN_SOURCE 700
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>