Make the function prototype visible to comply with C99 inline.

Fixes building with gcc -std=gnu99.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@14140 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/i386/idct_sse2_xvid.c

@@ -39,6 +39,7 @@
  */
 
 #include "libavcodec/dsputil.h"
+#include "libavcodec/i386/idct_xvid.h"
 
 /*!
  * @file idct_sse2_xvid.c