[clang] [HLSL] Implement the SV_IsFrontFace semantic (PR #221353)

[Finn Plummer via cfe-commits]

inbelic wrote:

Okay, sounds good. I will close it for now then but feel free to re-open or post a new pr if you find the time. Otherwise, I will pick it up when I get a chance. Thanks

https://github.com/llvm/llvm-project/pull/221353