This will allow us to make changes in QtCore itself, without having to
worry about moc compatibility.
The output uses an #ifdef so this version of moc can still be used to
compile earlier versions of Qt (usually, in cross-compilation
environments). See discussion in the mailing list[1].
[1] https://lists.qt-project.org/pipermail/development/2021-September/041732.html
Change-Id: I2de1b4dfacd443148279fffd16a39784c80c5f3b
Reviewed-by: Lars Knoll <lars.knoll@qt.io>