generates a warning about subclasses that add members but do not
override operator==()

Change-Id: If6df1a2cbd115f17bcca22f9b7995181dcf55c03
Reviewed-on: https://gerrit.libreoffice.org/20468Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>