* [libmpeg2] Add new port
Libmpeg2 seems to be a somewhat old project, last release was done in
2008, but it is still in use by some projects e.g. ResidualVM
I have verified the mpeg2dec built for x86-64 with MSVC produces similar
results as the one pre-packaged on my Arch.
* [libmpeg2] Apply review comments
* [libmpeg2] Add ci.baseline.txt exemptions
