replace XENOCARA_RERUN_AUTOCONF setting with autoreconf make target.

The previous mechanism didn't play well with the new separated build
user.

README

@@ -116,11 +116,8 @@ configure.ac mostly), you need to rebuild the configure script and
 makefiles skeletons. For that use the following command in the
 directory where you edited the autotools source files:
 
- doas env XENOCARA_RERUN_AUTOCONF=Yes make -f Makefile.bsd-wrapper build
-
-You can also set XENOCARA_RERUN_AUTOCONF in /etc/mk.conf or in the
-environment to force the regeneration of configure scripts
-in every component during a make build.
+ make autoreconf
+ doas make -f Makefile.bsd-wrapper build
 
 o Cleaning in packages managed by autotools
   -----------------------------------------
@@ -196,4 +193,4 @@ The core dump will be in /var/crash.
 See also <http://xorg.freedesktop.org/wiki/Development/Documentation/ServerDebugging>
 
 -- 
-$OpenBSD: README,v 1.37 2016/10/14 18:29:18 matthieu Exp $
+$OpenBSD: README,v 1.38 2017/02/12 18:19:54 matthieu Exp $

share/mk/bsd.xorg.mk

@@ -1,4 +1,4 @@
-# $OpenBSD: bsd.xorg.mk,v 1.57 2016/11/19 14:22:05 tb Exp $ -*- makefile  -*-
+# $OpenBSD: bsd.xorg.mk,v 1.58 2017/02/12 18:19:54 matthieu Exp $ -*- makefile  -*-
 #
 # Copyright © 2006,2012 Matthieu Herrb
 #
@@ -141,11 +141,11 @@ all:	config.status
 	@exec ${MAKE} ${_lt_libs}
 .endif
 
+autoreconf:
+	cd ${_SRCDIR}; ${AUTOTOOLS_ENV} exec autoreconf -v --install --force
+
 .if !target(config.status)
 config.status:
-.if defined(XENOCARA_RERUN_AUTOCONF) && ${XENOCARA_RERUN_AUTOCONF:L} == "yes"
-	cd ${_SRCDIR}; ${AUTOTOOLS_ENV} exec autoreconf -v --install --force
-.endif
 	${CONFIGURE_ENV} PATH=$(XENOCARA_PATH) \
 		exec sh ${_SRCDIR}/configure --prefix=${X11BASE} \
 		--sysconfdir=/etc \