[llvm] [offload] Extend LIT infrastructure to allow using more tools (PR #124636)

[Shilei Tian via llvm-commits]

shiltian wrote:

I think `clang/test/Tooling/` is indeed the right place.

> I didn't think I could assume OpenMP was available inside the clang project

What I see from this is, whatever (OpenMP, SYCL, HIP, or even CUDA) is got linked via `clang-linker-wrapper` doesn't matter. To test changes in `clang-linker-wrapper` you don't have to use OpenMP compilation. In addition, even if you really want to test OpenMP, you don't need a full compilation. We have tests for compiling OpenMP at different stages but we only have end-to-end test when it really needs to run and check the results.

https://github.com/llvm/llvm-project/pull/124636