Cygwin: serial: select: fix previous revamp patch

- We need a verify function.
- The event object referenced in WaitCommEvent must not be a local var,
  move it into fhandler_serial.

winsup/cygwin/fhandler.h

@@ -1685,6 +1685,7 @@ class fhandler_serial: public fhandler_base
   pid_t pgrp_;
   int rts;				/* for Windows 9x purposes only */
   int dtr;				/* for Windows 9x purposes only */
+  DWORD event;				/* for select */
 
  public:
   OVERLAPPED io_status;