[clang] [OpenMP][OMPIRBuilder] Add support to omp target parallel (PR #67000)

[via cfe-commits]

shraiysh wrote:

> @shraiysh `ParallelSimpleGPU` tests only the LLVM IR for the target device. `kmpc_parallel_51` is the function which needs to be executed on the GPU. The aim of this patch is to add GPU code generation for `omp target parallel pragma`.

Okay, I misunderstood the testcase a bit earlier. So, the function `func` is the kernel entry function which should be properly set at the host end while emitting IR. I suppose that is not a part of this patch.

This patch LGTM @kiranchandramohan (with Johannes' comments addressed). 

https://github.com/llvm/llvm-project/pull/67000