prevent exit missuse

Originally committed as revision 8536 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -55,6 +55,8 @@
 #define INFINITY HUGE_VAL
 #endif
 
+#undef exit
+
 /* select an input stream for an output stream */
 typedef struct AVStreamMap {
     int file_index;