Use the new configuration system to define external
libraries, configure tests and features. Don't use
pkg-config outside of the configuration step. And
move all command line options over from qtbase, so
that we can remove them from there in a second step.

Change-Id: I1aa4b557a6aee17eeceb00602005a2d28b426a26
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Yoann Lopes <yoann.lopes@qt.io>