[llvm] [PGO][Offload] Make PGO GPU tests atomic (PR #132262)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 approved this pull request.

Normal `pragma omp target` is a little weird since it executes with multiple threads but masks all of them off except one. It's somewhat possible that this would interact with something? Also, AFAIK, all aligned accesses on AMDGPU should be 'stomic' at least in terms out the output. If this lowers to fine-grained memory maybe not.

https://github.com/llvm/llvm-project/pull/132262