... except four instances in QCoreApplication that would conflict with
another change.
Replace a locally-defined MutexUnlocker with a call to unlock() +
qScopedGuard'ed lock() to avoid having to spell out the locker type
while we can't depend on C++17 CTAD, yet.
In QSettings, move the new mutex locker into and out of
initDefaultPaths(), such as is idiomatic for std::unique_lock, but
wasn't possible with QMutexLocker (which is not movable).
Change-Id: I23056e13ecaa76159db583c7dccc6e05715e0788
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
fd785c3899