build: Fix absl log flags being stripped

[joeyparrish]

According to a comment in
packager/third_party/abseil-cpp/source/absl/log/CMakeLists.txt, many linkers will strip the contents of absl::log_flags because its symbols symbols are only used in a global constructor, and that for now, clients should link using
$<LINK_LIBRARY:WHOLE_ARCHIVE,absl::log_flags>.

Closes #1325

[joeyparrish]

I believe I have the docker builds fixed with the latest commit. PTAL!

[cosmin]

The windows shared build is failing with a

LINK : fatal error LNK1104: cannot open file 'D:\a\shaka-packager\shaka-packager\build\packager\Release\libpackager.lib' [D:\a\shaka-packager\shaka-packager\build\packager\libpackager_static.vcxproj]

[joeyparrish]

The windows shared build is failing with...

I've seen that before, and it doesn't make much sense, unless there is a race condition in the parallel build. I think if I re-run the failed job, it will pass, which could also point toward timing.

[cosmin]

It's not clear why the shared windows build is trying to build libpackager static.

[joeyparrish]

It's not clear why the shared windows build is trying to build libpackager static.

It always builds static, but only builds shared in the shared configuration. This is ever since #1293, but I don't remember the reasoning behind it.

[joeyparrish]

I'm going to file a new issue to look into this build flake, and I'll mention changes to the target structure as an option.