[clang] [clang][flang][windows] Prefer user-provided library paths (-L) (PR #90758)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Thanks. Can you add a test? Possibly `clang/test/Driver/msvc-link.c`. 
`linux-cross.cpp` has a good example about how to test the default `-L` paths.

https://github.com/llvm/llvm-project/pull/90758