gl/cocoa: Disable hack for NSApp iteration with a special #define

gl/cocoa: Disable hack for NSApp iteration with a special #define

The hack causes deadlocks and other interesting problems and it really
can only be fixed properly inside GLib. We will include a patch for
GLib in our builds for now that handles this, and hopefully at some
point GLib will also merge a proper solution.

A proper solution would first require to refactor the polling in
GMainContext to only provide a single fd, e.g. via epoll/kqueue
or a thread like the one added by our patch. Then this single
fd could be retrieved from the GMainContext and directly integrated
into a NSRunLoop.

https://bugzilla.gnome.org/show_bug.cgi?id=741450
https://bugzilla.gnome.org/show_bug.cgi?id=704374