[llvm] [InstCombine] Fold fmod to frem if we know it does not set errno. (PR #107912)

[Matt Arsenault via llvm-commits]

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

LGTM, but this is ignoring the flags directly on the instruction. If I read this correctly, you can just do this for any nnan call 

https://github.com/llvm/llvm-project/pull/107912