[llvm] [Bazel] Add support for Bzlmod (PR #88927)

[Aaron Siddhartha Mondal via llvm-commits]

aaronmondal wrote:

I believe this is still blocked by these:

- https://github.com/bazelbuild/bazel/commit/6f254ce0f95d70e744b513a94d577036712befac, i.e. we currently don't have access to `new_local_repository` with non-nightly Bazel
- https://github.com/bazelbuild/bazel/issues/21592, i.e. the recent versions of Bazel that we'd need fail with "undeclared inclusions xxx.cppmap".

I just tried building with `8.0.0-pre.20240607.2` and `bazelisk test --config=ci @llvm-project//...` and it still failed because of that.

https://github.com/llvm/llvm-project/pull/88927