[llvm] [DAGCombiner] Port custom DAG combine for `rem` from NVPTX (PR #210344)

[Matt Arsenault via llvm-commits]

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arsenm wrote:

I wouldn't bother with the check and just update the test. It doesn't make sense to disable a specific combine at -O0, it needs to be applied globally. People have tried to disable DAGCombiner at -O0 before but it's never quite stuck 

https://github.com/llvm/llvm-project/pull/210344