calling QEventLoop::exit() from a different thread doesn't always exit the eventloop

Suppose you started a local run of a QEventLoop in some thread:

// thread1

QEventLoop loop;

loop.exec();

and you want to exit it from a different thread like this:

// thread2 gets a reference to the loop variable somehow

loopFromThread1.exit(0);

then the loop does not always exit.

The issue seems to be caused by the fact that the interrupt variable in QEventDispatcherWin32Private is a normal bool and not an atomic.
The change of the Boolean to false by the interrupt() call by QEventLoop::exit() is not always seen by the thread running the loop.

The same member has been turned into a QAtomicInt in QEventDispatcherUNIXPrivate by the following commit:

Ieffaa169eb67f40dc935291b3994f9ff1c7e05f0

https://codereview.qt-project.org/#/c/51060/