[llvm] Add constant-folding for unary NVVM intrinsics (PR #141233)

[Lewis Crawford via llvm-commits]

LewisCrawford wrote:

The lit-test failures for nvvm_round on PPC that this patch caused here: https://lab.llvm.org/buildbot/#/builders/64/builds/4929 should be fixed now by the follow-up patch in #149837 .

https://github.com/llvm/llvm-project/pull/141233