QmlDebugging: Force build for all Symbian targets

Don't stop if e.g. the build for the very first target winscw fails.

Change-Id: I9a8e06045340f2921018bcbe8d2587d848f9aa3f
Reviewed-on: http://codereview.qt.nokia.com/1944


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Alessandro Portale <alessandro.portale@nokia.com>