Sync with gnulib 6da37d4814fb6d1c61169de4092205a056a04a21.

Do not classify a bind-mounted dir entry as "dummy".

* m4.include/ls-mntd-fs.m4: Check for hasmntopt() on platforms with
1-argument getmntent() (instead of assuming absence).

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>