the arguments after '--' are by definition meant only for the top-level
project, as that's where configure is invoked from. passing them to
sub-projects just adds noise to the make output and misleads users.
note that this specifically does not support qmake -r, which will break
if the subprojects rely on the arguments being absent. this isn't a
problem, because the qt build doesn't support qmake -r anyway.
Change-Id: I7ecff6212ce3137526005fc324a4a7ae45e3345e
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>