The unifdef command appeared in 2.9BSD.  ANSI C support was added in FreeBSD 4.7.

The unifdef command was originally written by Dave Yost <Dave@Yost.com>.
Tony Finch <dot@dotat.at> rewrote it to support ANSI C.
The standalone 'unifdef' packaging was written by Bob Proulx <bob@proulx.com>.
