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

[Matt Arsenault via llvm-commits]

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arsenm wrote:

This is unworthy of an opt level check, this isn't an expensive optimization. The -O0 check would be somewhere else's responsibility 

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