QmlDesigner: fix compile for Qt 5

The itemlibrary ideally should not rely on private
headers. Fixing this requires heavy refactoring so
we rely on private headers for now.

Change-Id: If52c1254ac164995dbb667b5baa024635f6d3dc8
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
(cherry picked from commit b356ad96)
Reviewed-by: Marco Bubke <marco.bubke@digia.com>

src/plugins/qmldesigner/components/itemlibrary/itemlibrary.pri

@@ -13,3 +13,7 @@ OTHER_FILES += \
     qml/ItemView.qml \
     qml/ItemsViewStyle.qml \
     qml/ItemsView.qml
+
+greaterThan(QT_MAJOR_VERSION, 4) {
+    QT += quick1-private core-private script-private
+}