add FF_API_SYMVER define to disable symver compatibility functions

Originally committed as revision 25491 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avformat.h

@@ -81,6 +81,9 @@
 #ifndef FF_API_FIRST_FORMAT
 #define FF_API_FIRST_FORMAT            (LIBAVFORMAT_VERSION_MAJOR < 53)
 #endif
+#ifndef FF_API_SYMVER
+#define FF_API_SYMVER                  (LIBAVFORMAT_VERSION_MAJOR < 53)
+#endif
 
 /**
  * I return the LIBAVFORMAT_VERSION_INT constant.  You got

libavformat/utils.c

@@ -290,7 +290,7 @@ AVInputFormat *av_find_input_format(const char *short_name)
     return NULL;
 }
 
-#if LIBAVFORMAT_VERSION_MAJOR < 53 && CONFIG_SHARED && HAVE_SYMVER
+#if FF_API_SYMVER && CONFIG_SHARED && HAVE_SYMVER
 FF_SYMVER(void, av_destruct_packet_nofree, (AVPacket *pkt), "LIBAVFORMAT_52")
 {
     av_destruct_packet_nofree(pkt);