Enable cmake config files generation

As QtWebEngine now uses 5.x as its version number, we can just
provide cmake tests and let qmake scripts do the rest.

Task-number: QTBUG-42073
Change-Id: I28ccddbd1849980074dfbeefb5cb5a70c9209ab1
Reviewed-by: Andras Becsi <andras.becsi@theqtcompany.com>