Fix s390x symbol

Fix symbol for s390x from the build log.

debian/libqt5xdg3.symbols

@@ -137,7 +137,7 @@ libQt5Xdg.so.3 libqt5xdg3 #MINVER#
  (c++)"XdgMimeType::operator=(XdgMimeType const&)@Base" 1.0.0
  (c++)"XdgMimeType::~XdgMimeType()@Base" 1.0.0
  (c++)"XdgMimeType::swap(XdgMimeType&)@Base" 3.5.0
- (c++)"void std::vector<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >, std::allocator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > > >::_M_realloc_insert<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > >(__gnu_cxx::__normal_iterator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >*, std::vector<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >, std::allocator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > > > >, std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >&&)@Base" 3.5.0+git20201115
+ (optional|c++|arch= !s390x)"void std::vector<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >, std::allocator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > > >::_M_realloc_insert<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > >(__gnu_cxx::__normal_iterator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >*, std::vector<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >, std::allocator<std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> > > > >, std::unique_ptr<XdgDesktopFile, std::default_delete<XdgDesktopFile> >&&)@Base" 3.5.0+git20201115
  (c++)"non-virtual thunk to XdgMenuWidget::~XdgMenuWidget()@Base" 1.0.0
  (c++)"typeinfo for XdgAction@Base" 1.0.0
  (c++)"typeinfo for XdgDesktopFile@Base" 1.0.0