[clang] [llvm] Add processor aliases back to -print-supported-cpus and -mcpu=help (PR #118581)

[Tomas Matheson via llvm-commits]

https://github.com/tmatheson-arm approved this pull request.

I'm surprised how complicated this was to do, but LGTM.

https://github.com/llvm/llvm-project/pull/118581