include pedantic warnings fix

import the change from meekrosoft/fff#98
and see what happens

Author: mmitch

src/thirdparty/fff.h

@@ -26,6 +26,8 @@ SOFTWARE.
 #ifndef FAKE_FUNCTIONS
 #define FAKE_FUNCTIONS
 
+#pragma GCC system_header
+
 #include <stdarg.h>
 #include <string.h> /* For memset and memcpy */