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

[Jan Patrick Lehr via cfe-commits]

https://github.com/jplehr commented:

I looked at the changes and from the little I understand CMake they seem ok.
I added one nit.

Maybe @saiislam can have a look as well.

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