QCoreApplication: relax an atomic load in a Q_ASSERT()

A Q_ASSERT() must not have side-effects, incl. ordering memory. So the
implicit loadAcquire() was too strong. The code must also work with
loadRelaxed(), so use that.

Amends the start of the public history.

Pick-to: 6.10
Change-Id: Ib94bd0989d1a358b552275dc3963b014e6e4c180
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qcoreapplication.cpp

@@ -1951,7 +1951,7 @@ void QCoreApplication::removePostedEvents(QObject *receiver, int eventType)
 
 #ifdef QT_DEBUG
     if (receiver && eventType == 0) {
-        Q_ASSERT(!receiver->d_func()->postedEvents);
+        Q_ASSERT(!receiver->d_func()->postedEvents.loadRelaxed());
     }
 #endif