Add '#include "libavutil/intreadwrite.h"', necessary for AV_RB32.

This fixes the build with demuxers disabled.

Originally committed as revision 20327 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mp3.c

@@ -21,6 +21,7 @@
 
 #include <strings.h>
 #include "libavutil/avstring.h"
+#include "libavutil/intreadwrite.h"
 #include "avformat.h"
 #include "id3v2.h"
 #include "id3v1.h"