[llvm] [llvm-objdump] Support --mcpu=help/--mattr=help without -d (PR #165661)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

You still need to update the PR description to reflect the final changes (in particular --mattr=help support).

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