[llvm] [libc] add multi-platform pre-commit github actions (PR #119104)

[Tom Stellard via llvm-commits]

tstellar wrote:

> I can see that the cache writing run into errors but I don't know why. Perhaps github forbids some writes when update the cache too frequently. For the time being, I guess this is already the best caching effort I can do with sccache.

I'm not sure what kind of errors you are seeing but for the other jobs we've been using a different action for managing the sccache and it's working pretty well: https://github.com/llvm/llvm-project/blob/main/.github/workflows/llvm-project-tests.yml#L93

https://github.com/llvm/llvm-project/pull/119104