[clang] [flang] [Driver] Ensure ToolChain::LibraryPaths is not empty for non-Darwin (PR #88661)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Thanks for the `-resource-dir=` suggestion, but I think we can push this part separately to make tests more stable.
I am landing it separately and will than reland #87866   without changing the commit message

https://github.com/llvm/llvm-project/pull/88661