[llvm] [DXIL] Add sign intrinsic part 2 (PR #101988)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

> @farzonl This seems good to go. I cannot merge this myself though. I will take some time later today to rebase this PR on main.

Let me get one more reviewer from my team to take a look and then I'll merge it for you. Thanks again. Also thank you for your patience.

https://github.com/llvm/llvm-project/pull/101988