This fixes linking on MinGW after the library renaming, and is also
in line with the logic in the nmake generator.
Change-Id: Ie25ce6c1d2b8f292c4e454db1cad9bcbbee7a05d
Suggested-by: Erik van Pienbroek
Task-number: QTBUG-27137
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>