Remove the last in-tree user of qExchange() and mark all of Qt free of it

We've ported all qExchange() to std::exchange by now, across all
modules, but the one in QScopedValueRollback was left behind, because
it requires C++20's version of std::exchange (constexpr).

Since q20::exchange was not approved, replace the qExchange() here
with two moves and add a comment to port to std::exchange() once we
can depend on C++20.

Then add QT_NO_QEXCHANGE to avoid new uses from creeping in.

Change-Id: I488e252433e78fb2766639dbe77a22a55196cfd1
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

0 files changed, 0 insertions, 0 deletions