Fix warning caused by warning fix

qevent.h:865:36: error: unknown warning group '-Wunused-private-field', ignored [-Werror,-Wunknown-pragmas]

Instead, just use Q_UNUSED() like I've done for the other unused
members.

Change-Id: I3adeb06937cee8b8ac24a1d5081be03931ac98b7
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

src/gui/kernel/qevent.cpp

@@ -4217,6 +4217,7 @@ void QTouchEvent::TouchPoint::setFlags(InfoFlags flags)
 QScrollPrepareEvent::QScrollPrepareEvent(const QPointF &startPos)
     : QEvent(QEvent::ScrollPrepare), m_target(0), m_startPos(startPos)
 {
+    Q_UNUSED(m_target);
 }
 
 /*!

src/gui/kernel/qevent.h

@@ -860,14 +860,7 @@ public:
     void setContentPos(const QPointF &pos);
 
 private:
-#ifdef Q_CC_CLANG
-#  pragma clang diagnostic push
-#  pragma clang diagnostic ignored "-Wunused-private-field"
-#endif // Q_CC_CLANG
     QObject* m_target; // Qt 6 remove.
-#ifdef Q_CC_CLANG
-#  pragma clang diagnostic pop
-#endif // Q_CC_CLANG
     QPointF m_startPos;
     QSizeF m_viewportSize;
     QRectF m_contentPosRange;