[clang] [CIR] Upstream support for name mangling (PR #137094)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

Seems alright so far.    Though if we're going to add the CUDA global, we should have a test for it.

https://github.com/llvm/llvm-project/pull/137094