* autoload.cc (WSAIoctl): Reintroduce.

(WSASendMsg): Define.
	* fhandler.h (class fhandler_socket): Change definition of recv_internal
	and send_internal to take WSAMSG pointer as parameter.
	* fhandler_socket.cc (WSAID_WSARECVMSG): Define.
	(LPFN_WSARECVMSG): Define.
	(WSASendMsg): Declare.
	(get_ext_funcptr): New function to fetch address of WSARecvMsg.
	(fhandler_socket::recv_internal): Take just a LPWSAMSG parameter.
	Change code accordingly.  If control information is requested,
	fetch address of WSARecvMsg and use that instead of WSARecvFrom.
	(fhandler_socket::recvfrom): Change return type to ssize_t as
	declared in fhandler.h.  Accommodate changes to recv_internal.
	(fhandler_socket::recvmsg): Ditto.  Make sure that control information
	is only requested if system, address family, and socket type support it.
	(fhandler_socket::send_internal): Take just a LPWSAMSG parameter
	and the flags.  Change code accordingly.  If control information is
	provided, use WSASendMsg instead of WSASendTo.
	(fhandler_socket::sendto): Drop useless comment.  Accommodate changes
	to send_internal.
	(fhandler_socket::sendmsg): Ditto.  Make sure that control information
	is only provided if system, address family, and socket type support it.
	* wincap.h (wincaps::has_recvmsg): New element.
	(wincaps::has_sendmsg): New element
	* wincap.cc: Implement above elements throughout.
	* include/cygwin/socket.h (CMSG_ALIGN): Phrase in terms of alignment
	of type struct cmsghdr.

winsup/cygwin/include/cygwin/socket.h

@@ -80,7 +80,8 @@ struct cmsghdr
 };
 
 #define CMSG_ALIGN(len) \
-	(((len) + sizeof (size_t) - 1) & ~(sizeof (size_t) - 1))
+	(((len) + __alignof__ (struct cmsghdr) - 1) \
+	 & ~(__alignof__ (struct cmsghdr) - 1))
 #define CMSG_LEN(len) \
 	(CMSG_ALIGN (sizeof (struct cmsghdr)) + (len))
 #define CMSG_SPACE(len) \