Fix DateTime with recent versions of tzdata

An backport of http://trac.webkit.org/changeset/150833 needed for
correct time KRAT, YAKT and MOS timezones.

Task-number: QTBUG-41422
Change-Id: I6e9d1db690fee8d77faa1d76c836bd7b345ce854
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>