[llvm] [offload] Fix finding amdgpu/nvptx-arch to generate tests (PR #135072)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

I'm unsure why the change would cause it to no longer emit to `bin/`. We still emit those programs but as symlinks. The existing test for the target already wouldn't work in a non-projects build so it's probably just silently acting like it did before.

https://github.com/llvm/llvm-project/pull/135072