Don't assume SO_UPDATE_CONNECT_CONTEXT is defined.

asio/include/asio/detail/impl/socket_ops.ipp

diff --git a/asio/include/asio/detail/impl/socket_ops.ipp b/asio/include/asio/detail/impl/socket_ops.ipp
index c601210..6b06013 100644
--- a/asio/include/asio/detail/impl/socket_ops.ipp
+++ b/asio/include/asio/detail/impl/socket_ops.ipp
@@ -529,8 +529,9 @@
     // Need to set the SO_UPDATE_CONNECT_CONTEXT option so that getsockname
     // and getpeername will work on the connected socket.
     socket_ops::state_type state = 0;
+    const int so_update_connect_context = 0x7010;
     socket_ops::setsockopt(s, state, SOL_SOCKET,
-        SO_UPDATE_CONNECT_CONTEXT, 0, 0, ec);
+        so_update_connect_context, 0, 0, ec);
   }
 }