libio: Fix deadlock between freopen, fflush (NULL) and fclose (bug 24963)

libio: Fix deadlock between freopen, fflush (NULL) and fclose (bug 24963)

The canonical lock ordering for stream list processing is
locking list_all_lock first, then individual streams as needed.
The fclose implementation reversed that, and the freopen
implementation performed list operations under the reverse order,
too.

Unlinking in fclose was already unconditional, and the early unlinking
looks unnecessary: _IO_file_close_it would call it even for
!_IO_IS_FILEBUF streams.

There is still a remaining concurrency defect because
_IO_new_file_init_internal links in the stream before it is
fully initialized, and it is not locked at this point.

Reviewed-by: Arjun Shankar <arjun@redhat.com>