[clang] [OpenMP] Allow GPUs to be targeted directly via `-fopenmp`. (PR #122149)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I don't think it should be GPU code generation path as there is no explicit `target` region used.

it needs to be, otherwise the code generation for things like `#pragma omp parallel` will be wrong. The way I see it, the DeviceRTL is `libomp.a` for the GPU target, so we need to emit runtime calls for that runtime.

https://github.com/llvm/llvm-project/pull/122149