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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> @jhuber6 , looks like these changes break the following builds
> 
>     * https://lab.llvm.org/buildbot/#/builders/235/builds/5630
> 
>     * https://lab.llvm.org/buildbot/#/builders/232/builds/19808
> 
> 
> there are a lot of CMake error messages started with
> 
> ```
> CMake Error at cmake/modules/AddLLVM.cmake:631 (set_target_properties):
>   set_target_properties called with incorrect number of arguments.
> Call Stack (most recent call first):
>   cmake/modules/AddLLVM.cmake:854 (llvm_add_library)
>   lib/Transforms/Hello/CMakeLists.txt:13 (add_llvm_library)
> -- Targeting X86
> -- Targeting NVPTX
> CMake Error at CMakeLists.txt:1213 (add_subdirectory):
>   add_subdirectory given source "/unittest" which is not an existing
>   directory.
> CMake Error at tools/llvm-config/CMakeLists.txt:54 (string):
>   string sub-command REGEX, mode MATCH needs at least 5 arguments total to
>   command.
> ...
> ```
> 
> would you take care of it?

I'll look into it, my guess is that I used `LLVM_DEFAULT_TARGET_TRIPLE` instead of one of the runtime ones or something.

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