[clang] [llvm] [OpenMP] Adds omp_target_is_accessible routine (PR #138294)

[Nicole Aschenbrenner via cfe-commits]

nicebert wrote:

@carlobertolli can you review this. I've reworked the patch using hsa_amd_pointer_info as we discussed.

@CatherineMoore FIY

https://github.com/llvm/llvm-project/pull/138294