message: Add abbreviated name for Debugger::EventHandlerThread.
  On OS's where thread names are limited to 16 bytes, the full name was truncated to not very meaningful "r.event-handler".
diff: @@ -1586,15 +1586,18 @@ bool Debugger::StartEventHandlerThread() {
  // is up and running and listening to events before we return from this
  // function. We do this by listening to events for the
  // eBroadcastBitEventThreadIsListening from the m_sync_broadcaster
  - ListenerSP listener_sp(
  - Listener::MakeListener("lldb.debugger.event-handler"));
  + ConstString full_name("lldb.debugger.event-handler");
  + ListenerSP listener_sp(Listener::MakeListener(full_name.AsCString()));
  listener_sp->StartListeningForEvents(&m_sync_broadcaster,
  eBroadcastBitEventThreadIsListening);
  + auto thread_name =
  + full_name.GetLength() < llvm::get_max_thread_name_length() ?
  + full_name.AsCString() : "dbg.evt-handler";
  +
  // Use larger 8MB stack for this thread
  - m_event_handler_thread = ThreadLauncher::LaunchThread(
  - "lldb.debugger.event-handler", EventHandlerThread, this, nullptr,
  - g_debugger_event_thread_stack_bytes);
  + m_event_handler_thread = ThreadLauncher::LaunchThread(thread_name,
  + EventHandlerThread, this, nullptr, g_debugger_event_thread_stack_bytes);
  // Make sure DefaultEventHandler() is running and listening to events
  // before we return from this function. We are only listening for events of
  