qmake relies heavily on stable references to nodes stored within the
container. QHash in Qt6 doesn't offer that guarantee, so use a QMap
instead, that supports this.
Change-Id: Ifcf3d67098585ea26f4e02f4570d407a56e33c9c
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>