It's used to handle qCritical() messages, and corresponds to QtMsgType's
QtCriticalMsg, so change its name to reflect what it really is.
In the process, reclassify the -maxwarnings overflow message as a warning,
rather than a critical message.
Pick-to: 6.2
Change-Id: I87626117a547ae4498d5dc352b93bd6db8bfb332
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>