Bootstrap etcupdate(8) as part of the release build, similar

to what is done for mergemaster(8).  This allows etcupdate(8)
to work out-of-box after the first upgrade of a system.

Submitted by:	jhb
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation

release/Makefile

@@ -104,6 +104,8 @@ base.txz:
 # Set up mergemaster root database
 	sh ${.CURDIR}/scripts/mm-mtree.sh -m ${WORLDDIR} -F \
 	    "TARGET_ARCH=${TARGET_ARCH} TARGET=${TARGET}" -D "${.OBJDIR}/${DISTDIR}/base"
+	etcupdate extract -B -M "TARGET_ARCH=${TARGET_ARCH} TARGET=${TARGET}" \
+	    -d "${.OBJDIR}/${DISTDIR}/base/var/db/etcupdate"
 # Package all components
 	cd ${WORLDDIR} && ${IMAKE} packageworld DISTDIR=${.OBJDIR}/${DISTDIR}
 	mv ${DISTDIR}/*.txz .