Generate configure before calling ./configure --help

Change-Id: I21a88802b6ca617a44def3bc96789eb97969c918
Reviewed-on: https://gerrit.libreoffice.org/6291
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>