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

[via llvm-commits]

valadaptive wrote:

SimplifyLibCalls is a huge mess right now. There are some functions that try to optimize a libcall and return the corresponding intrinsic as a last resort, there are some that try to optimize a libcall and just bail out entirely if the optimization doesn't work, and there are some (like `optimizeSymmetricCall`) that optimize to *other libcalls* and then exit early because, well, the optimization worked.

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