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

[Farzon Lotfi via llvm-commits]

farzonl wrote:

> I don't have commit access so feel free to merge this for me.

I will. Our current policy on HLSL is two approvals. So I’m waiting for a second one.

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