mangle on mingw32 patch by ("Sascha Sommer" <saschasommer at freenet dot de>)

Originally committed as revision 1721 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/libpostproc/mangle.h

@@ -8,7 +8,7 @@
 #define __MANGLE_H
 
 /* Feel free to add more to the list, eg. a.out IMO */
-#if defined(__CYGWIN__) || defined(__OS2__) || \
+#if defined(__CYGWIN__) || defined(__MINGW32__) || defined(__OS2__) || \
    (defined(__OpenBSD__) && !defined(__ELF__))
 #define MANGLE(a) "_" #a
 #else