Only define LIBVLC_USED for GCC 3.4 or newer. GCC 3.3 does not support the...

Only define LIBVLC_USED for GCC 3.4 or newer. GCC 3.3 does not support the warn_unused_result attribute.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 09a2365da0672be3e8401f6fcafd765b281db3ad)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

include/vlc_common.h

@@ -80,7 +80,11 @@
 #     define LIBVLC_FORMAT(x,y) __attribute__ ((format(printf,x,y)))
 #   endif
 #   define LIBVLC_FORMAT_ARG(x) __attribute__ ((format_arg(x)))
-#   define LIBVLC_USED __attribute__ ((warn_unused_result))
+#   if __GNUC__ > 3 || (__GNUC__ == 3 && (__GNUC_MINOR__ >= 4))
+#     define LIBVLC_USED __attribute__ ((warn_unused_result))
+#   else
+#     define LIBVLC_USED
+#   endif
 #   define LIBVLC_MALLOC __attribute__ ((malloc))
 #else
 #   define LIBVLC_FORMAT(x,y)