[libcxx-commits] [libcxx] Refactor dockerfile to support Buildkite AND Github Actions (PR #71954)

[Louis Dionne via libcxx-commits]

ldionne wrote:

> I think this LGTM once `run-buildbot-container` is updated and we make sure it still works!

NVM, this was updated but I was looking at an outdated trunk.

https://github.com/llvm/llvm-project/pull/71954