[clang] [llvm] [OpenMP] Don't reserve the generic mode warp on SPIR-V (PR #222763)

[Nick Sarnie via cfe-commits]

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

Thanks, this is basically the same patch I had in-progress here https://github.com/llvm/llvm-project/pull/222712 which I will close now

https://github.com/llvm/llvm-project/pull/222763