The build fails with Clang 6 and soon the port will be marked as BROKEN on 12.0 and 11.2 if we do not act.
Created attachment 196514 [details] mbox2mdir.diff
A commit references this bug: Author: acm Date: Mon Aug 27 05:59:26 UTC 2018 New revision: 478177 URL: https://svnweb.freebsd.org/changeset/ports/478177 Log: - Fix build PR: 230879 Submitted by: tobik Changes: head/mail/mbox2mdir/Makefile head/mail/mbox2mdir/files/ head/mail/mbox2mdir/files/patch-mbox2mdir.cpp