[clang] [offload-arch] Fix HIP DLL discovery and loading on Windows (PR #194063)

[Jacob Lambert via cfe-commits]

lamb-j wrote:

Do we need to update clang/unittets/CMakeLists.txt to call add_subdirectory(offload-arch)?

Also is the test going to get tripped up on "extern cl::opt<bool> Verbose;"?

https://github.com/llvm/llvm-project/pull/194063