Ok turns out we still want to keep the rc_bg variable around but we need

to know which daemon cannot background themselves (actually we want to
know the opposite, but there are much more). However, it's only needed in
_rc_wait and rc.subr still does its magic without the need to add `&'.

src/etc/rc.d/rc.subr

@@ -1,4 +1,4 @@
-#	$OpenBSD: rc.subr,v 1.119 2017/05/27 13:51:52 ajacoutot Exp $
+#	$OpenBSD: rc.subr,v 1.120 2017/05/27 19:55:48 ajacoutot Exp $
 #
 # Copyright (c) 2010, 2011, 2014-2017 Antoine Jacoutot <ajacoutot@openbsd.org>
 # Copyright (c) 2010, 2011 Ingo Schwarze <schwarze@openbsd.org>
@@ -91,7 +91,8 @@ _rc_wait() {
 	if [ X"$1" = X"start" ]; then # prevent hanging the boot sequence
 		trap "_rc_alarm" ALRM
 		while [ $_i -lt ${daemon_timeout} ]; do
-			_rc_do rc_check && break
+			_rc_do rc_check && [ X"${rc_bg}" = X"YES" ] && break ||
+				[ -z "$$" ] && break
 			sleep 1
 			_i=$((_i+1))
 		done & wait

src/etc/rc.d/ypbind

@@ -1,11 +1,12 @@
 #!/bin/sh
 #
-# $OpenBSD: ypbind,v 1.6 2017/05/27 13:51:52 ajacoutot Exp $
+# $OpenBSD: ypbind,v 1.7 2017/05/27 19:55:48 ajacoutot Exp $
 
 daemon="/usr/sbin/ypbind"
 
 . /etc/rc.d/rc.subr
 
+rc_bg=YES
 rc_reload=NO
 
 rc_pre() {