[llvm] [X86][GlobalISel] Support G_FCMP for scalar cases (PR #123598)

[Simon Pilgrim via llvm-commits]

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

LGTM - if you're after jobs, we should probably try to use `legalFor` in more places in X86LegalizerInfo.cpp

https://github.com/llvm/llvm-project/pull/123598