[llvm] [OpenMP] Port the OpenMP device runtime to direct C++ compilation (PR #123673)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Do you plan to have a follow-up that addresses the concerns about the explicit address space numbers? I too think it would be easier to read if some sort of enum is used instead of plain numbers.

Yes, I'm going to port this stuff to use `gpuintrin.h` instead so future architectures just need to define that header's definitions.

https://github.com/llvm/llvm-project/pull/123673