[clang] [llvm] [SPIR-V] Add builtin/intrinsic for subgroup ballot (PR #174862)

[Farzon Lotfi via cfe-commits]

https://github.com/farzonl requested changes to this pull request.

This can reuse the work HLSL did in the spirv instruction selector\ spirv intrinsics.

https://github.com/llvm/llvm-project/pull/174862