* src/assuan-defs.h (w32_fdpass_recv): New.
* src/assuan-socket-server.c (assuan_init_socket_server): Use it.
* src/system-w32.c (get_file_handle): New.
(w32_fdpass_send): Implement.
(process_fdpass_msg): Implement.
(w32_fdpass_recv): New.
(__assuan_read): De-multiplex the sendfd message and normal message.