Avoid warnings from AV_GCC_VERSION_AT_LEAST with some non-gcc compilers

Originally committed as revision 17508 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/common.h

@@ -35,7 +35,11 @@
 #include <stdlib.h>
 #include <string.h>
 
-#define AV_GCC_VERSION_AT_LEAST(x,y) (defined(__GNUC__) && (__GNUC__ > x || __GNUC__ == x && __GNUC_MINOR__ >= y))
+#ifdef __GNUC__
+#    define AV_GCC_VERSION_AT_LEAST(x,y) (__GNUC__ > x || __GNUC__ == x && __GNUC_MINOR__ >= y)
+#else
+#    define AV_GCC_VERSION_AT_LEAST(x,y) 0
+#endif
 
 #ifndef av_always_inline
 #if AV_GCC_VERSION_AT_LEAST(3,1)