[llvm] [Github] Build PGO optimized toolchain in container (PR #80096)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

The container ends up being 808MB fully unpacked. It's only a couple hundred MB in download size (not sure what the full one is currently). I think that should probably be fine. I've seen pretty good performance improvements with just this configuration (~20% when I last tested it), but it's not the theoretical max. I think we can land this, start moving jobs over to the container, and then once some other patches land, we can do better perf-training and see what the results are like.

https://github.com/llvm/llvm-project/pull/80096