[llvm] [NFC][LLVM] Namespace cleanup in MSCVPaths (PR #163779)

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

I don't see the reason for this change. The commit message also doesn't explain why this is being done. The use of the scoped `llvm` seems reasonable to me, and avoids unnecessary indentation.

https://github.com/llvm/llvm-project/pull/163779