Without this patch, trying to build latte-dock with clang 9.0 results in:

`../app/settings/delegates/persistentmenu.cpp:23:41: error: addition of default argument on redeclaration makes this constructor a default constructor
PersistentMenu::PersistentMenu(QWidget *parent = 0)

^        ~

../app/settings/delegates/persistentmenu.h:31:3: note: previous declaration is here

PersistentMenu(QWidget *parent);
^

1 error generated.
`

Install clang 9.0-rc1, try to build latte-dock, see if it succeeds