To make TCP listening properly multithreaded, we need to have the
uv_export() and uv_import() functions that were removed from libuv.
The alternative is passing sockets over IPC, which is complicated and
error prone.

To make it simple, we export two internal functions from libuv; they will
be used in lib/isc/netmgr/uv-compat.c by our versions of the uv_export()
and uv_import() functions.

diff --git a/src/win/internal.h b/src/win/internal.h
index 058ddb8e..a9dc4168 100644
--- a/src/win/internal.h
+++ b/src/win/internal.h
@@ -92,11 +92,11 @@ void uv_process_tcp_connect_req(uv_loop_t* loop, uv_tcp_t* handle,
 void uv_tcp_close(uv_loop_t* loop, uv_tcp_t* tcp);
 void uv_tcp_endgame(uv_loop_t* loop, uv_tcp_t* handle);
 
-int uv__tcp_xfer_export(uv_tcp_t* handle,
+UV_EXTERN int uv__tcp_xfer_export(uv_tcp_t* handle,
                         int pid,
                         uv__ipc_socket_xfer_type_t* xfer_type,
                         uv__ipc_socket_xfer_info_t* xfer_info);
-int uv__tcp_xfer_import(uv_tcp_t* tcp,
+UV_EXTERN int uv__tcp_xfer_import(uv_tcp_t* tcp,
                         uv__ipc_socket_xfer_type_t xfer_type,
                         uv__ipc_socket_xfer_info_t* xfer_info);