Introduce QT6_VIRTUAL and QT6_NOT_VIRTUAL macros

To avoid QT_VERSION_CHECK ifdefs

Change-Id: I364903964c72f4df19b8b7c10c19b82d24f63600
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/global/qglobal.h

@@ -88,6 +88,11 @@
 
 #if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
 #  define QT_NO_UNSHARABLE_CONTAINERS
+#  define QT6_VIRTUAL virtual
+#  define QT6_NOT_VIRTUAL
+#else
+#  define QT6_VIRTUAL
+#  define QT6_NOT_VIRTUAL virtual
 #endif
 
 /* These two macros makes it possible to turn the builtin line expander into a

src/widgets/graphicsview/qgraphicsscene.h

@@ -288,11 +288,7 @@ protected:
                            QWidget *widget = nullptr);
 
 protected Q_SLOTS:
-    // ### Qt 6: make unconditional
-#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
-    virtual
-#endif
-    bool focusNextPrevChild(bool next);
+    QT6_VIRTUAL bool focusNextPrevChild(bool next);
 
 Q_SIGNALS:
     void changed(const QList<QRectF> &region);

src/widgets/kernel/qlayout.h

@@ -126,8 +126,8 @@ public:
     bool isEmpty() const override;
     QSizePolicy::ControlTypes controlTypes() const override;
 
-    // ### Qt 6 make this function virtual
-    QLayoutItem *replaceWidget(QWidget *from, QWidget *to, Qt::FindChildOptions options = Qt::FindChildrenRecursively);
+    QT6_VIRTUAL QLayoutItem *replaceWidget(QWidget *from, QWidget *to,
+                                           Qt::FindChildOptions options = Qt::FindChildrenRecursively);
 
     int totalHeightForWidth(int w) const;
     QSize totalMinimumSize() const;

src/xml/sax/qxml.h

@@ -122,10 +122,8 @@ public:
     QXmlAttributes &operator=(const QXmlAttributes &) = default;
     QXmlAttributes &operator=(QXmlAttributes &&) Q_DECL_NOTHROW = default;
 #endif // default members
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
-    virtual // ### Qt 6: this value class don't need no virtual dtor
-#endif
-    ~QXmlAttributes();
+
+    QT6_NOT_VIRTUAL ~QXmlAttributes();
 
     void swap(QXmlAttributes &other) Q_DECL_NOTHROW
     {