[clang] [llvm] [HLSL] Handle WaveActiveBallot struct return type appropriately (PR #175105)

[Finn Plummer via cfe-commits]

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

LGTM once a test of lowering the llvm intrinsic to dxil op with the scalarizer is added. 

https://github.com/llvm/llvm-project/pull/175105