[llvm] [offload] [test] Skip amdgcn/nvptx tests if detected arch is not built (PR #119006)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Hmm, except that `plugins-nextgen` is built before `DeviceRTL`, so we don't have the list there yet. No clue if they can be safely reordered.

Don't think they depend on eachother, they used to a long time ago.

https://github.com/llvm/llvm-project/pull/119006