Current version in ports is 6.10 from 2012, but the latest version is 6.12 from Dec. 2014.
Created attachment 161911 [details] update testbuilds on 11a, 10.2a+i, 9.3a are fine.
A commit references this bug: Author: pi Date: Sun Oct 11 14:29:06 UTC 2015 New revision: 399088 URL: https://svnweb.freebsd.org/changeset/ports/399088 Log: www/squidclamav: 6.10 -> 6.13 - Unbreak - Update - Changes: http://squidclamav.darold.net/news.html PR: 198274 Approved by: mm (timeout) Changes: head/www/squidclamav/Makefile head/www/squidclamav/distinfo head/www/squidclamav/files/patch-etc-Makefile.in head/www/squidclamav/files/patch-etc_Makefile.in head/www/squidclamav/pkg-plist
HTH.
Please merge it to 2015Q4, it's marked as BROKEN there