New port: shells/oksh

oksh is the portable version of the OpenBSD Korn shell, a continuation
of the Public Domain Korn Shell (PDKSH). Its command language is a
superset of the sh(1) shell language. oksh is best known as the
default user shell and /bin/sh on OpenBSD.

WWW: https://devio.us/~bcallah/oksh/

PR: 225097
Submitted by: Brian Callahan <bcallah@openbsd.org>