[llvm] [runtimes] Skip custom linker validation for gpu/offload targets (PR #189933)

[Wenju He via llvm-commits]

wenju-he wrote:

Hi, I have updated this PR to add a baseline test to first check if the target can link executable. If the baseline test fails (typical for gpu/offload), we skip the custom linker validation.
So there should be no risk for non-offload cross-build: the custom linker is still validated for targets that can link executable.
Please review again, thanks.

https://github.com/llvm/llvm-project/pull/189933