no-thread: Add dummy implementations for stackSize functions in QThread

We recently added a call to setStackSize() in the QML thread, which
revealed that the dummy implementation for this function was missing
in no-thread builds.

Fixes: QTBUG-79571
Change-Id: Ibabb48d9cba73afda0842642045a2961e65523f9
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/corelib/thread/qthread.cpp

@@ -919,6 +919,16 @@ QThreadPrivate::~QThreadPrivate()
     delete data;
 }
 
+void QThread::setStackSize(uint stackSize)
+{
+    Q_UNUSED(stackSize);
+}
+
+uint QThread::stackSize() const
+{
+    return 0;
+}
+
 #endif // QT_CONFIG(thread)
 
 /*!