[libunwind] [libunwind] Fix libunwind library path for runtime test (PR #110777)

[via cfe-commits]

zeroomega wrote:

Test run on our downstream bot: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci.shadow/clang-linux-x64/b8735236964550803665/overview

This patch should address the build failure introduced in PR #110171

https://github.com/llvm/llvm-project/pull/110777