Example fails to link on macOS

[ct-porco]

I'm unable to fully build the included example on macOS. Cargo fails during the linking step. (The example builds fine as-is on Debian.) I've found that adding a build.rs file like the one below resolves the linking issue. I'm happy to put it in a pull request if that's helpful. This also appears to be a required step to build crates which depend on wsdf on macOS.

fn main() {
    #[cfg(target_os = "macos")]
    {
        println!("cargo:rustc-link-arg=-undefined");
        println!("cargo:rustc-link-arg=dynamic_lookup");
    }
}