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

[Finn Plummer via cfe-commits]

https://github.com/inbelic commented:

I would like to see if there is another reviewer has a suggestion of how we could re-use the built-in

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