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

[Farzon Lotfi via llvm-commits]

farzonl wrote:

The SPIRV test case isn't sufficent. Two reasons.

1. Since you are not using `__builtin_addc ` Your codegen path for `uadd.with.overflow` is custom to HLSL. Your emitter is in `EmitHLSLBuiltinExpr`.
2. `llvm/test/CodeGen/SPIRV/llvm-intrinsics/uadd.with.overflow.ll` only tests `spirv32` and `spirv64` targets when HLSL uses the `spirv` target

You can add a `spirv` target to `uadd.with.overflow.ll`. Make sure nothing blows up if we use our target. 
Second a test case in the hlsl_intrinsics directory is warranted to make sure the custom things you are doing like `CreateShuffleVector` doesn't trigger and problems for spirv codegen or for the spirv validator `spirv-val`.

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