[clang] [llvm] Add cross builtins and cross HLSL function to DirectX and SPIR-V backend (PR #109180)

[Greg Roth via cfe-commits]

https://github.com/pow2clk approved this pull request.

Looks good to me. I just have a couple nits that you might include if you create another commit for another reason. 

https://github.com/llvm/llvm-project/pull/109180