* fhandler.h (fhandler_serial::fhandler_serial): Change to only accept unit

argument.
* fhandler_serial.cc (fhandler_serial::fhandler_serial): Ditto.
(fhandler_serial::open): Avoid else when previous clause is a return().
* path.cc (get_devn): Alias /dev/ttyS0 -> /dev/com1, etc.
(get_device_number): Reallow standalone "com1" as a valid name for /dev/com1.

winsup/cygwin/fhandler.h

@@ -159,7 +159,6 @@ class fhandler_base
 {
 protected:
   DWORD status;
-public:
 private:
   int access;
   HANDLE io_handle;
@@ -579,7 +578,7 @@ public:
   OVERLAPPED io_status;
 
   /* Constructor */
-  fhandler_serial (DWORD devtype = FH_SERIAL, int unit = 0);
+  fhandler_serial (int unit);
 
   int open (path_conv *, int flags, mode_t mode);
   int close ();