lavu: add an API function to return the Libav version string

This returns something like "v12_dev0-1332-g333a27c". This is much more
useful than the individual library versions, of which there are too
many, and which are very hard to map back to releases or git commits.

Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavutil/utils.c

@@ -19,11 +19,18 @@
 #include "config.h"
 #include "avutil.h"
 
+#include "avversion.h"
+
 /**
  * @file
  * various utility functions
  */
 
+const char *av_version_info(void)
+{
+    return LIBAV_VERSION;
+}
+
 unsigned avutil_version(void)
 {
     return LIBAVUTIL_VERSION_INT;