Move _GNU_SOURCE declaration further to the top, so recursive inclusion of stdio does not ignore the macro

ot_http.c

@@ -4,9 +4,9 @@
    $id$ */
 
 /* System */
+#define _GNU_SOURCE
 #include <arpa/inet.h>
 #include <pthread.h>
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>