[llvm] [workflows] Port buildkite Windows config to GitHub actions (PR #82093)

[Mehdi Amini via llvm-commits]

https://github.com/joker-eph requested changes to this pull request.

> Unlike buildkite, which tested everything, this new workflow only tests clang, llvm, and lld due to resource constraints on the GitHub runners.

I do have very strong concerns about this: it does not seem acceptable to me to make steps in a direction where it make it seems that there are two classes of support in the project between subprojects.

https://github.com/llvm/llvm-project/pull/82093