Qt::WFlags is obsolete in Qt5. Replace it with Qt::WindowFlags.

This change is Qt4/Qt5 neutral.

src/Gui/DlgPreferencesImp.cpp

@@ -58,7 +58,7 @@ std::list<DlgPreferencesImp::TGroupPages> DlgPreferencesImp::_pages;
  *  The dialog will by default be modeless, unless you set 'modal' to
  *  TRUE to construct a modal dialog.
  */
-DlgPreferencesImp::DlgPreferencesImp( QWidget* parent, Qt::WFlags fl )
+DlgPreferencesImp::DlgPreferencesImp( QWidget* parent, Qt::WindowFlags fl )
     : QDialog(parent, fl), ui(new Ui_DlgPreferences), canEmbedScrollArea(true)
 {
     ui->setupUi(this);