NetBSD has had it for 11 years. FreeBSD has had it for three years and six months. DragonFly doesn't have it, OpenBSD doesn't have it...
http://cvsweb.netbsd.org/bsdweb.cgi/src/usr.bin/cal/cal.c?re... http://svnweb.freebsd.org/base?view=revision&revision=204697