[clang] [Driver] Ensure ToolChain::LibraryPaths is not empty for non-Darwin (PR #87866)

[via cfe-commits]

estewart08 wrote:

Is it expected now that `clang --print-runtime-dir` will always have the clang host triple appended even if `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR` is off?

https://github.com/llvm/llvm-project/pull/87866