[llvm] [DirectX] Allow llvm.assume intrinsic to pass on to DXIL (PR #165311)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

Just a note, we will want to use the offload test suite to see  if the AMD, Intel, Nvidia, and Qualcomm gpu drivers can handle the assume llvm intrinsic. If they can't we should just remove this intrinsic. But for now we will allow it to pass on so we can run experiments. I can confirm right now that the metal tests are working with `llvm.assume`.

https://github.com/llvm/llvm-project/pull/165311