Add support for the Linux/m68k platform

Add necessary support code to recognize m68k as an architecture;
use GCC builtin atomics like avr32 does. Copy avr32 header, since
it was hinted that including it from m68k was not liked.

This is not needed in Qt5 because it’s said to automatically use
the GCC atomic builtins.

Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=660963

Task-number: QTBUG-28237
Change-Id: I6c51405c47549c904899a6971b6cd34b8239c642
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Move the declaration of QFileIconProviderPrivate to it's own file.

Needed to backport qtbase/46685f755b01288fd53c4483cb97a22c426a57f0
to Qt4.

We can't add new symbols in Qt4 to QFileIconProvider so we will make
the private class a friend of the QFileDialog.

Change-Id: Ic720d681da14698ecf8557e1223d82bda6b33e23
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
(cherry picked from qtbase/f4a0d6d2494d1dd41cd5b854a48b435120714d32)