Currently we build tests as long as the libraries are found on the
machine. This doesn't necessarily mean there is a GPU to use though.
This patch changes it to where we only will build the tests if we found
a compatible GPU via `nvptx-arch` or `amdgpu-arch`.
The only downside to this I could see if someone were to build LLVM on a
home node of a cluster and then wished to run the tests after switching
to a compute node. For this I think we should allow it to be overridden.
I think that's better than allowing us to run tests that will fail by
default.
Reviewed By: tianshilei1992
Differential Revision: https://reviews.llvm.org/D142018
ea0eee80d8