An int is used in the end anyway for all cases
(Dialog::add_button for the VCL implementations,
QtBuilder::set_response for the Qt implementation).
Change-Id: I3011f25d465edaed23ab1a312c6a424ee2d51198
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/182045
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Tested-by: Jenkins