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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

It's definitely not ideal that this prints a non-existent path if the per-target runtime directory configuration is off. Couldn't we just do a trivial filesystem check to make sure it exists before appending it?

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