[clang] [llvm] [HLSL] [DXIL] Implement the `AddUint64` HLSL function and the `UAddc` DXIL op (PR #125319)

[Farzon Lotfi via llvm-commits]

https://github.com/farzonl requested changes to this pull request.

needs `DirectXTargetTransformInfo.cpp` change and coresponding vector to scalarization tests before I can sign off. but this is very close.

https://github.com/llvm/llvm-project/pull/125319