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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

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

I'll update it, but will still need the clang flavored builtin. I'll use the existing intrinsic but define a new clang builtin, but I also question why we call these things `wave` when that's not the SPIR-V naming convention.

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