add private export to image and rectangle nodes

Change-Id: I15aea1b1dc3d41c9efe0a38f53d6858bae273566
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/quick/scenegraph/qsgdefaultimagenode_p.h

@@ -60,7 +60,7 @@ protected:
     virtual QSGMaterialShader *createShader() const;
 };
 
-class QSGDefaultImageNode : public QSGImageNode
+class Q_QUICK_PRIVATE_EXPORT QSGDefaultImageNode : public QSGImageNode
 {
 public:
     QSGDefaultImageNode();

src/quick/scenegraph/qsgdefaultrectanglenode_p.h

@@ -63,7 +63,7 @@ protected:
     virtual QSGMaterialShader *createShader() const;
 };
 
-class QSGDefaultRectangleNode : public QSGRectangleNode
+class Q_QUICK_PRIVATE_EXPORT QSGDefaultRectangleNode : public QSGRectangleNode
 {
 public:
     QSGDefaultRectangleNode();