QFrame: add unit test

This test shows a behavior change of setFrameStyle(QFrame::WinPanel)
between 4.4 and 4.5.
Turns out that 4.4 defaulted to "Raised" only via a side effect of the
code, while 4.5 defaults to "Plain" which makes more sense since Plain
is the default anyway. So there is no actual bug to fix (the app code
really meant QFrame::WinPanel|QFrame::Raised anyway), but the unittest
is still good to have for the future.

Done-with: David Faure
Change-Id: Icf16382504b18357256bc601b1e865abac9f2b2a
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
QFrame: introduce initStyleOption (and use it)

For some reason lost in time QFrame was missing that method. Of course
that led to duplicated code and to subtle sizing miscalculations.

Task-number: QTBUG-29330
Change-Id: I81163f5def6661e01cb2ecc49c1169449a3e3758
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Import forkfd into qtbase

forkfd is a tool that I designed to facilitate spawning
sub-processes. It's implemented in C, not C++, so that it could be
used by other libraries as well.

To work in all platforms Qt supports and with all compilers Qt is
known to work with, we'll need to replace the generic GCC atomics that
are provided here.

Change-Id: I0a6f86cc220a7c52c8d4284bb7140c56d5cf836a
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>