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

[Jon Chesterfield via llvm-commits]

https://github.com/JonChesterfield commented:

This changes way too much at once. I saw the missed annotation on shared but the signal to noise makes reviewing difficult. I note that some tests are failing with the change, seems a credible risk the IR in different as a result.

A large fraction of this should be pure NFC, as in the IR before and after are literally identical, and landing that first would make seeing / understanding the other changes much easier.

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