Make the default style "Base" when built without widgets support
Make the default style "Base" when built without widgets support

It is possible to have qtwidgets installed but qtquickcontrols built
without a dependency to qtwidgets.

Change-Id: Ic6f640e352984d38d9020011078fe061ff46acac
Reviewed-by: Gabriel de Dietrich <57b5c683f0b6abfc17ef151d5b68c8944258b63a@digia.com>

mizukusak/qtquickcontrols,mizukusak/qtquickcontrols,mizukusak/qtquickcontrols