[llvm] [Offload] Skip most liboffload tests if no devices (PR #157417)

[Michał Górny via llvm-commits]

https://github.com/mgorny commented:

Thanks for doing this. It's a bit verbose, but as long as the tests pass, I'm happy with it. Just one small comment.

https://github.com/llvm/llvm-project/pull/157417