[clang] [openmp] [OpenMP] Respect LLVM per-target install directories (PR #83282)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> @jhuber6 unfortunately after [2fb764d](https://github.com/llvm/llvm-project/commit/2fb764d2dae288f24335dfc168b5491a1017fc83)
> 
> ```
> ls /soft/compilers/llvm/master-nightly/lib/x86_64-unknown-linux-gnu/libomptarget.rtl*
> /soft/compilers/llvm/master-nightly/lib/x86_64-unknown-linux-gnu/libomptarget.rtl.cuda.so          /soft/compilers/llvm/master-nightly/lib/x86_64-unknown-linux-gnu/libomptarget.rtl.x86_64.so
> /soft/compilers/llvm/master-nightly/lib/x86_64-unknown-linux-gnu/libomptarget.rtl.cuda.so.19.0git  /soft/compilers/llvm/master-nightly/lib/x86_64-unknown-linux-gnu/libomptarget.rtl.x86_64.so.19.0git
> ```
> 
> amdgpu plut is missing.

This is confusing. I have it in my local install no problem and the `install` code is pretty much the exact same between the CUDA and AMDGPU plugins. Can you share what CMake you're using?

https://github.com/llvm/llvm-project/pull/83282