[llvm] [bazel] Add MODULE.bazel (PR #164891)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

If there are no objections, I'll land this a bit later. Happy to fix forward or revert if it causes downstream issues.

> sounds good, fwiw there is still a behavior difference here that downstream projects cannot influence the version used by llvm with the current solution. so you can use the same one but you can't use a newer point release etc until we do that

Not sure what situation you're describing. Since these files live in tree, it's inherently tied to an LLVM version anyway. Do you mean someone would use this MODULE.bazel config but supply their own LLVM sources, either pinned to a different version or just forked from the same version, and this approach would not allow that?

https://github.com/llvm/llvm-project/pull/164891