IOV_MAX alternative for the Hurd?

OpenNTPd uses IOV_MAX 
<https://github.com/openntpd-portable/openntpd-openbsd/blob/master/src/lib/libutil/imsg-buffer.c> 
which is not defined on the Hurd, and the wiki doesn't have any 
instructions on what is the alternative to this.

It does mention how to fix code which uses PATH_MAX and HOST_NAME_MAX, 
but not IOV_MAX. Any guides on how to do it?