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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> @aeubanks The problem is that in your configure, the libclang_rt is placed in `<builddir>/lib/clang/19/lib/linux/libclang_rt.builtins-arm-android.a`, instead of `<buildir>/lib/clang/19/lib/arm-unknown-linux-android/libclang_rt.builtins.a`.

The point is that both locations were supposed to be accepted, as they were before - this PR was not supposed to be a policy change that affects that.

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