Fix all remaining warnings in gp2x build. The compiler is a bit more picky about the includes and feature macros.

git-svn-id: svn://pulkomandy.tk/GrafX2/trunk@1352 416bcca6-2ee7-4201-b75f-2eb2f807beb1

buttons.c

@@ -19,9 +19,12 @@
     You should have received a copy of the GNU General Public License
     along with Grafx2; if not, see <http://www.gnu.org/licenses/>
 */
+#define _XOPEN_SOURCE 500
+
 #include <fcntl.h>
 #include <stdio.h>
 #include <string.h>
+#include <strings.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <ctype.h>