fchmodat does not support this flag - symlinks do not have permissions.

Sysadmin probably does not expect us to not follow symlinks either:
if /var -> /mnt/foo/var, we should be making sure the permissions
and ownership is correct on the target directory, not on the symlink.

Since fchmodat never returned ENOENT with AT_SYMLINK_NOFOLLOW, this
also fixes directory re-creation if it does not exist. fixes #1348.