[clang] [llvm] [HLSL] Adding HLSL `clip` function. (PR #114588)

[Farzon Lotfi via cfe-commits]

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

Minor comments, but rest LGTM. Code correct as ticket is currently defined.  We may want to move the behavior you currently have in cgbuiltins to hlsl_intrinsics.h. That way for spirv instead of a basic block we could do a c++ if statement. That can wait though until the team finalizes our plan.

https://github.com/llvm/llvm-project/pull/114588