Don't set h_errno on MS-Windows except in gethostbyname.
See http://lists.gnu.org/archive/html/emacs-devel/2013-02/msg00293.html
and the following discussion for the details.
src/w32.c (set_errno): Reset h_errno and don't set it to any other
value. Set errno instead.
(check_errno): Reset h_errno.
(sys_socket, socket_to_fd, sys_bind, sys_connect)
(sys_gethostname, sys_getservbyname, sys_getpeername)
(sys_shutdown, sys_setsockopt, sys_listen, sys_getsockname)
(sys_accept, sys_recvfrom, sys_sendto, fcntl, sys_read): Don't set
h_errno.
(sys_gethostbyname): Set h_errno only errors detected.