[llvm] [InstCombine] Declare command line options in TableGen (PR #227948)

[Alexis Engelke via llvm-commits]

https://github.com/aengelke approved this pull request.

LGTM, but please give the usual InstCombine folks a chance/few days to look at this.

https://github.com/llvm/llvm-project/pull/227948