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

[Ingo Müller via llvm-commits]

ingomueller-net wrote:

How can downstream projects consume LLVM as dependency using bzlmod from the git repository?

I have tried something like this but I am struggling with setting up the overlay correctly:

```bzl
bazel_dep(name = "llvm-project-overlay")
local_path_override(
    module_name = "llvm-project-overlay",
    path = "third_party/llvm-project/utils/bazel",
)
```

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