Enable building Qt5 through --include-dependencies

Currently kdesrc-build actively blocks building Qt in the dependency resolver: See: modules/ksb/DependencyResolver:139

        # Ignore deps on Qt, since we allow system Qt.
        next if $sourceItem =~ /^\s*Qt/ || $dependentItem =~ /^\s*Qt/;

This issue also covers BUG 404484 on b.k.o: https://bugs.kde.org/show_bug.cgi?id=404484 This is also why 'fixing' the 'typo' in the kde-build-metadata appeared to fix this, see abandoned diff D19171 on phabricator.kde.org: https://phabricator.kde.org/D19171