add QT_CONFIG's static/shared to CONFIG on startup

... instead of as a fallback in default_post.
it was this way in qt4, and it requires less code to be written in the
end. we are already doing it for debug/release as well.

Change-Id: I6e02849d61d14a18375cf64a5990768931ebac48
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>