Seems like the new audio channel api was not as backwards compatible as we thought.
Therefore we need to reintroduce the usage of the old api to make older ffmpeg version be able to compile Blender.
This change is only intended to stick around for two releases or so. After that we hope that most Linux distros ship
ffmpeg >=5.0 so we can switch to it.
Reviewed By: Sergey
Differential Revision: http://developer.blender.org/D16408
Mainly caused by moving tests to source folder, which brings
new compiler flags.
Also, no need to extend include directories (to the non-existing paths,
btw) since this is done by the CmakeList.txt which is in the blenlib folder.
And make them part of the blender_test runner. The one exception is blenlib
performance tests, which we don't want to run by default. They remain in their
own executable.
Differential Revision: https://developer.blender.org/D8498
