wince: vsnprintf is not available, use qvsnprintf

Change-Id: I42c87b2c319ce5b530ac5dc673edc99b067fafd7
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Andreas Holzammer <andreas.holzammer@kdab.com>
Reviewed-by: Björn Breitmeyer <bjoern.breitmeyer@kdab.com>