Fix warnings from adding -Wall back
diff --git a/compositor/compositor.c b/compositor/compositor.c
index f993bf6..ee5b9aa 100644
--- a/compositor/compositor.c
+++ b/compositor/compositor.c
@@ -16,6 +16,8 @@
  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  */
 
+#define _GNU_SOURCE
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>