Blender Git Loki

Fix T70514: VP9 not working

This issue was two-fold:

- In the VPX library build script: missing `--enable-vp8` and
`--enable-vp9` meant that the choice to enable these codecs or not was
left to the library's `configure` script, rather than an explicit choice.
On the build-bot it chose to not enable them.
- Missing pkgconfig paths passed to the FFmpeg build script

Thanks @brecht for helping out.