Merge "clang/win: Make libvpx build with -Wunused-function."

vpx/vpx_codec.h

@@ -69,7 +69,7 @@ extern "C" {
 
   /*!\brief Decorator indicating a function is potentially unused */
 #ifdef UNUSED
-#elif __GNUC__
+#elif defined(__GNUC__) || defined(__clang__)
 #define UNUSED __attribute__ ((unused))
 #else
 #define UNUSED