meson: ensure native platform is one of the undetectable ones
We've had a bunch of people reporting issues with X11 apps not working caused by bad configuration on their part, especially after !2637 (merged) fixed the bug that would select X11 regardless of what the user had configured.
Let's make sure the native platform is one of the undetectable ones, ie. x11, surfaceless, haiku, or android, so that nobody makes that same mistake again.