Cygwin: AF_UNIX: store per-socket info in shared memory

Per-socket info in fhandler isn't correctly shared between multiple
instances of th same descriptor.  Implement a basic shared info which
is shared between all instances of a socket.

This also requires to move the fhandler_socket status bits into
fhandler_socket_wsock since the data is moved to the shared region
for AF_UNIX sockets.

Also, drop backing file requirement for socketpair server socket.
This will be handled differently in recvmsg/sendmsg.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_socket_inet.cc

@@ -201,6 +201,7 @@ fhandler_socket_wsock::fhandler_socket_wsock () :
   wsock_events (NULL),
   wsock_mtx (NULL),
   wsock_evt (NULL),
+  status (),
   prot_info_ptr (NULL)
 {
   need_fork_fixup (true);