9l: refactor the warning-silencing mechanics to match that of 9c

bin/9c

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-test -f $PLAN9/config && . $PLAN9/config
+test -f "$PLAN9/config" && . "$PLAN9/config"
 usegcc()
 {
 	cc=${CC9:-gcc}
@@ -52,7 +52,7 @@ quiet()
 	ignore=$ignore'|warn_unused_result'
 	ignore=$ignore'|expanded from macro'
 
-	grep -v '__p9l_autolib_' $1 |
+	grep -v '__p9l_autolib_' "$1" |
 	egrep -v "$ignore" |
 	sed 's/ .first use in this function.$//; s/\"\([^\"][^\"]*\)\", line \([0-9][0-9]*\)/\1:\2/g' |
 	$(which uniq) 1>&2  # avoid built-in uniq on SunOS
@@ -143,10 +143,10 @@ case "$tag" in
 	exit 1
 esac
 
-# N.B. Must use temp file to avoid pipe; pipe loses status.
+# Must use temp file to avoid pipe; pipe loses status.
 xtmp=${TMPDIR-/tmp}/9c.$$.$USER.out
-$cc -DPLAN9PORT -I$PLAN9/include $cflags "$@" 2>$xtmp
+$cc -DPLAN9PORT -I"$PLAN9/include" $cflags "$@" 2>"$xtmp"
 status=$?
-quiet $xtmp
-rm -f $xtmp
+quiet "$xtmp"
+rm -f "$xtmp"
 exit $status