rewrite top-level configures without perl

otherwise the whole no-syncqt-and-thus-perl-needed stunt in qtbase would
be fairly useless for top-level builds.

Task-number: QTBUG-31786
Change-Id: I9f9b38091155a2d50ffec169267e0363fc24d3c0
Reviewed-by: Tuukka Turunen <tuukka.turunen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>