Pass -dead_strip to the native linker like we do for legacy Xamarin:
* If there are no custom linker arguments.
* If all third-party bindings in the app has SmartLink = true (this doesn't
show up in the PR, but the logic exists for legacy Xamarin and is already
executed for .NET, the resulting Application.DeadStrip value just wasn't
taken into account).
This shrinks the app size a bot for a Hello World app:
* Before: 10.659.731 (https://gist.github.com/rolfbjarne/b5892a5c7fb8663d38e2b69f67bce90c)
* After: 9.940.240 (https://gist.github.com/rolfbjarne/8404394180fb9971bd2f1475b747c70a)
* Difference: -719.491 (-6.7 %)