[llvm] [SelectionDAG] Handle roundeven libcall in visitCall (PR #170690)

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valadaptive wrote:

With https://github.com/llvm/llvm-project/pull/171288 fully committing to the opposite direction, this can be closed. Not sure about https://github.com/llvm/llvm-project/pull/170696; `hasOptimizedCodegen` is called in a few different places besides SelectionDAG.

https://github.com/llvm/llvm-project/pull/170690