GtkWindow: Enlarge the type hint private field
GtkWindow: Enlarge the type hint private field

Make it what it is - the enum - so that that it is sure that the hint
will fit in the field. Without this, any hint that doesn't fit in 3
bits will be truncated to the 3 least significant bits, causing
unexpected behaviour.

https://bugzilla.gnome.org/show_bug.cgi?id=756496

alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita