[llvm] [update_mir_test_checks] Add missing MIFlags (PR #150012)

[Jay Foad via llvm-commits]

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

LGTM

As an alternative could we assume that any lower case string is an MIFlag and that instruction names are in upper case? Or would that be too fragile?

https://github.com/llvm/llvm-project/pull/150012