Gui: put private class to anonymous namespace

src/Gui/propertyeditor/PropertyItem.cpp

@@ -2847,6 +2847,8 @@ void PropertyEnumItem::setValue(const QVariant& value)
     setPropertyValue(data);
 }
 
+namespace  {
+
 class EnumItems;
 
 struct EnumItem {
@@ -2875,6 +2877,8 @@ void EnumItem::populate(QMenu *menu)
         item.populate(subMenu);
 }
 
+} // anonymous namespace
+
 QWidget* PropertyEnumItem::createEditor(QWidget* parent, const QObject* receiver, const char* method) const
 {
     const std::vector<App::Property*>& items = getPropertyData();