[llvm] [llvm-objdump] Add triple support to `mcpu=help` (PR #165661)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

I'm afraid your test cases have gone rather wide of what I was expecting - the previous version was much closer, if I'm honest.

https://github.com/llvm/llvm-project/pull/165661