the check whether we are building a lib or an app (and thus have a target)
is done by quite some feature files (and generally wrongly, as they do not
account for the new aux target), so centralize it in default_post.prf.
Change-Id: I868edbc4185be8a6c23ecd4a2c126024d73cdeb4
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>