t7063: drop non-POSIX argument "-ls" from find(1)

Since commit 6b7728db81, (t7063: work around FreeBSD's lazy mtime
update feature, 2016-08-03), we started to use ls as a trick to update
directory's mtime.

However, `-ls` flag isn't required by POSIX's find(1), and
busybox(1) doesn't implement it.

Use "-exec ls -ld {} +" instead.

Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7063-status-untracked-cache.sh

@@ -18,7 +18,7 @@ GIT_FORCE_UNTRACKED_CACHE=true
 export GIT_FORCE_UNTRACKED_CACHE
 
 sync_mtime () {
-	find . -type d -ls >/dev/null
+	find . -type d -exec ls -ld {} + >/dev/null
 }
 
 avoid_racy() {