[llvm] [Utils][update_mc_test_checks] Support updating round-trip tests. (PR #164425)

[Brox Chen via llvm-commits]

broxigarchen wrote:

LGTM.

I feel this feature a little hidden in the script. Should we add a help option to list all the supported substitution and what it is trying to do?

https://github.com/llvm/llvm-project/pull/164425