Move /sys symlink creating out of etc/Makefile.

This is prep for etc/Makefile going away.

Approved by:	bapt (mentor)

Makefile.inc1

@@ -1239,6 +1239,7 @@ distributeworld installworld stageworld: _installcheck_world .PHONY
 	    METALOG=${METALOG} ${IMAKE_INSTALL} ${IMAKE_MTREE} \
 	    DISTBASE=/base DESTDIR=${DESTDIR}/${DISTDIR}/base \
 	    LOCAL_MTREE=${LOCAL_MTREE:Q} distrib-dirs
+	${INSTALL_SYMLINK} usr/src/sys ${DESTDIR}/sys
 .endif
 	${_+_}cd ${.CURDIR}; ${IMAKE} re${.TARGET:S/world$//}; \
 	    ${IMAKEENV} rm -rf ${INSTALLTMP}

etc/Makefile

@@ -386,7 +386,6 @@ distrib-dirs: ${MTREES:N/*} distrib-cleanup .PHONY
 		    ${METALOG.add} ; \
 	done; true
 .endif
-	${INSTALL_SYMLINK} usr/src/sys ${DESTDIR}/sys
 .if ${MK_NLS} != "no"
 	set - `grep "^[a-zA-Z]" ${.CURDIR}/nls.alias`; \
 	while [ $$# -gt 0 ] ; do \