PR #134713, which landed as 79cb6f05da37, causes this on my test
systems:
```
-- Building AMDGPU plugin for dlopened libhsa
-- Not generating AMDGPU tests, no supported devices detected. Use 'LIBOMPTARGET_FORCE_AMDGPU_TESTS' to override.
-- Building CUDA plugin for dlopened libcuda
-- Not generating NVIDIA tests, no supported devices detected. Use 'LIBOMPTARGET_FORCE_NVIDIA_TESTS' to override.
```
The problem is it cannot locate amdgpu-arch and nvptx-arch. This patch
enables it to.
I suspect there is more cleanup to do here. amdgpu-arch and nvptx-arch
do not appear to exist as cmake targets anymore, but there is still
cmake code here that looks for those targets.
5709506de0