[clang] [clang] Language to String function (PR #69487)

[Ulrich Weigand via cfe-commits]

uweigand wrote:

This is intended to be used by the z/OS target, see the patch here: https://github.com/llvm/llvm-project/pull/68926

I asked Yusra to pull this part out into a separate PR.

https://github.com/llvm/llvm-project/pull/69487