chatgui: add SetConsoleCtrlHandler for reliable Ctrl-C on Windows

tools/chatgui/transport/utun_node.cpp

@@ -44,6 +44,11 @@ static void signal_handler(int sig) {
     if (g_signal_ua) uasync_wakeup(g_signal_ua);
 }
 
+extern "C" void utun_node_signal_shutdown(void) {
+    g_shutdown = 1;
+    if (g_signal_ua) uasync_wakeup(g_signal_ua);
+}
+
 UtunNode::UtunNode(QObject* parent) : QObject(parent) {}
 
 UtunNode::~UtunNode() {