Can't load shared library on NetBSD

When attempting to run the `hello-world-dl` example on NetBSD 9.3, I get this error:

```
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: OpenError { kind: Library, detail: "opening library failed (/home/jtnunley/Testing/x11-rs/target/debug/examples/hello-world-dl: Shared object \"libX11.so.6\" not found); opening library failed (/home/jtnunley/Testing/x11-rs/target/debug/examples/hello-world-dl: Shared object \"libX11.so\" not found)" }', x11-dl/examples/hello-world-dl.rs:17:39
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

This is probably related to psychon/x11rb#785, in that both are probably the result of `libtool` producing different outputs.