Serialize access to the info/dir file; needed for parallel installs.

Reported by:	scottl

I'm not very fond of using the non-standard lockf(1) here, but I
have no better idea at the moment.  NetBSD uses ln(1) to create a
lock file, but this approach can result in a deadlock if make is
interrupted, leaving an orphaned lock file.

Makefile.inc1

@@ -522,7 +522,7 @@ distributeworld installworld: installcheck
 	mkdir -p ${INSTALLTMP}
 	for prog in [ awk cap_mkdb cat chflags chmod chown \
 	    date echo egrep find grep install-info \
-	    ln make mkdir mtree mv pwd_mkdb rm sed sh sysctl \
+	    ln lockf make mkdir mtree mv pwd_mkdb rm sed sh sysctl \
 	    test true uname wc zic; do \
 		cp `which $$prog` ${INSTALLTMP}; \
 	done

share/mk/bsd.info.mk

@@ -145,6 +145,7 @@ ${x:S/$/${ICOMPRESS_EXT}/}:	${x}
 .for x in ${INFO}
 INSTALLINFODIRS+= ${x:S/$/-install/}
 ${x:S/$/-install/}:
+	lockf -k ${DESTDIR}${INFODIR}/${INFODIRFILE} \
 	${INSTALLINFO} ${INSTALLINFOFLAGS} \
 	    --defsection=${INFOSECTION} \
 	    --defentry=${INFOENTRY_${x}} \