Use native bswap32 instruction when __CPU__ is x86_64 instead of generic 386 code.

Originally committed as revision 5049 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/bswap.h

@@ -27,7 +27,7 @@ static always_inline uint16_t bswap_16(uint16_t x)
 
 static always_inline uint32_t bswap_32(uint32_t x)
 {
-#if __CPU__ > 386
+#if __CPU__ != 386
  __asm("bswap   %0":
       "=r" (x)     :
 #else