[clang] [llvm] [HLSL] [DXIL] Implement the AddUint64 HLSL function and the UAddc DXIL op (PR #127137)

[Finn Plummer via cfe-commits]

https://github.com/inbelic commented:

Just copying over some comments from the previous p, that might not be completely resolved for new reviewers to consider.

https://github.com/llvm/llvm-project/pull/127137