gtk: Allow to disable all gtk-related libs
gtk: Allow to disable all gtk-related libs

RevBy: TrustMe
Use qmake CONFIG+=nogtk to disable building the GTK+ input context module and
the glib-based application support libraries.

I got annoyed that CONFIG+=disable-gtk-cache-update still installs the IM
module.

Full, original commit at 7008b819990111c7cdde9852e4975b15a8109090 in maliit-framework

maliit/inputcontext-gtk,maliit/inputcontext-gtk