dvdsubdec: allow compilation with -DDEBUG

Originally committed as revision 14212 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dvdsubdec.c

@@ -440,6 +440,8 @@ static int find_smallest_bounding_rectangle(AVSubtitle *s)
 
 #ifdef DEBUG
 #undef fprintf
+#undef perror
+#undef exit
 static void ppm_save(const char *filename, uint8_t *bitmap, int w, int h,
                      uint32_t *rgba_palette)
 {