libavmod build error

[kiufta]

ffmpeg 5.1 seems to be incompatible:

  CC       libavmod_la-mod_av.lo
mod_av.c:52:38: warning: ISO C forbids forward references to 'enum' types [-Wpedantic]
   52 | int mod_av_lockmgr_cb(void **m, enum AVLockOp op)
      |                                      ^~~~~~~~
mod_av.c:52:38: warning: 'enum AVLockOp' declared inside parameter list will not be visible outside of this definition or declaration
mod_av.c:52:47: error: parameter 2 ('op') has incomplete type
   52 | int mod_av_lockmgr_cb(void **m, enum AVLockOp op)
      |                                 ~~~~~~~~~~~~~~^~
mod_av.c: In function 'mod_av_lockmgr_cb':
mod_av.c:62:22: error: 'AV_LOCK_CREATE' undeclared (first use in this function); did you mean 'AV_LOG_TRACE'?
   62 |                 case AV_LOCK_CREATE:
      |                      ^~~~~~~~~~~~~~
      |                      AV_LOG_TRACE
mod_av.c:62:22: note: each undeclared identifier is reported only once for each function it appears in
mod_av.c:72:22: error: 'AV_LOCK_OBTAIN' undeclared (first use in this function)
   72 |                 case AV_LOCK_OBTAIN:
      |                      ^~~~~~~~~~~~~~
mod_av.c:79:22: error: 'AV_LOCK_RELEASE' undeclared (first use in this function)
   79 |                 case AV_LOCK_RELEASE:
      |                      ^~~~~~~~~~~~~~~
mod_av.c:86:22: error: 'AV_LOCK_DESTROY' undeclared (first use in this function)
   86 |                 case AV_LOCK_DESTROY:
      |                      ^~~~~~~~~~~~~~~

[seven1240]

see https://lists.freeswitch.org/pipermail/freeswitch-dev/2022-September/007964.html

[fx02]

Use ffmeg v6 and build with this patch: #2202

[Korynkai]

@fx02 While my patch may allow it to build, it may also cause undefined behavior. I had requested testing and investigation in that issue. If anybody has thoroughly tested this patch, please let me know so I may start a pull request. I have only just regained the ability to test Freeswitch due to equipment circumstances.