Building quickwidgets fails with "Unknown module(s) in QT: quick-private"

qtdeclarative/src/quickwidgets depends on quick-private.

qtdeclarative/src/src.pro uses different conditions for building the quick and the quickwidgets subdirs. If quick is not build, qmake on qtdeclarative/src/quickwidgets/quickwidgets.pro fails with:

Unknown module(s) in QT: quick-private

The attached patch shows a possible solution.

The issue is a triggered here in a minimal build for getting qcollectiongenerator (which doesn't really need a GUI, so I don't want to add more GL).