[clang] [libc] [llvm] [openmp] [libc] Rework the GPU build to be a regular target (PR #81921)

[Jon Chesterfield via cfe-commits]

https://github.com/JonChesterfield commented:

Stalled on https://github.com/llvm/llvm-project/pull/81557, trying to remove the approve mark as otherwise i'll forget about this

https://github.com/llvm/llvm-project/pull/81921