[llvm] [AMDGPU] Fix unittest linking error with `LLVM_LINK_LLVM_DYLIB` (PR #91727)

[Janek van Oirschot via llvm-commits]

JanekvO wrote:

Hey, thank you for the patch!
I'm actually not against removing the unittest altogether as described in https://github.com/llvm/llvm-project/pull/88257#issuecomment-2104633180. What I'm trying to test should be possible in a couple patches through regular regression tests. Do let me know if there's a preference to keep such a unittest in, though!

https://github.com/llvm/llvm-project/pull/91727