To enable the current Qt version to use a qt.conf that is independent
from the previous version, a file named 'qt<major-version>.conf' is
searched for first. If this file does not exist, a file with the
name 'qt.conf' is searched for.
Task-number: QTBUG-88635
Change-Id: If75b63f72a7bdbdf1de7729ea4ecb00810b58d12
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>