[Development] Breaking up QtPlatformSupport

[Jørgen Lind]

> This will be hard to do with qmake, so the easier way out is to remove the .a 
> altogether and use .pri files only. That requires moving the Wayland platform 
> plugin back into qtbase.
> 
Pretty please with sugar on top, do NOT do this. I understand that you
only see the "Wayland" side of things, But there are loads of people
interested in not having their plugin in the Qt source code. Using the
pri approach is STUPID! The hacks you will force upon people is just
not nice! We have been there, and we don't want to go back. Lets just
keep/"add again" the -l flags, and let configure figure out if their going
to be included or not.

Building platform plugins outside the Qt source tree IS a usecase we'r
going to support. Not only because of QtWayland but because there might
be someone developing ie. an ios plugin that they don't want to have inside
QtBase. People might have special HW that where they just write a plugin
to do special ioctl to controll the display. We don't want all plugins to
be in QtBase but more importantly we can expect all plugins to be in
QtBase.

Jørgen