Adds linux-generic-g++ which can be used for simple cross-building to
well-behaved Linux targets.
Change-Id: I20423249cbcaaf7fc2c65e46b737e682d9222e38
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
