[llvm] [OpenMP] Replace most GPU helpers with ones from <gpuintrin.h> (PR #125771)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> The stack seems messed up

I haven't landed the first commit yet so just ignore it, waiting in @ronlieb to let me know that it's not broken.

https://github.com/llvm/llvm-project/pull/125771