glib2 windows cmake: set root paths for dependencies
webkit windows: disable X11 related configurations

But WebKitGTK requires X server! I give up to cross compile for Windows
for now. :<
webkit windows: disable
gtk2: (maybe) fix wrong property value on ppc64 and s390x

GitHub: fixes #256

Reported by mtasaka. Thanks!!!
Update 2.2.1 entry