[clang] [OFFLOAD] Introduce libdevice function declarartions for future use for math OpenMP wrappers (PR #182215)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 commented:

I don't really know enough about SPIR-V to tell if this is correct or not

https://github.com/llvm/llvm-project/pull/182215