exit(3): Add HISTORY section

PR:		240259
Submitted by:	Gordon Bergling
Obtained from:	OpenBSD
Differential Revision:	https://reviews.freebsd.org/D24146

lib/libc/stdlib/exit.3

@@ -32,7 +32,7 @@
 .\"     @(#)exit.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd May 28, 2018
+.Dd March 22, 2020
 .Dt EXIT 3
 .Os
 .Sh NAME
@@ -131,3 +131,8 @@ and
 .Fn _Exit
 functions conform to
 .St -isoC-99 .
+.Sh HISTORY
+The
+.Fn exit
+function appeared in
+.At v1 .