Cygwin: pty: Make sure to show system error messages

- Forcibly attach to pseudo console in advance so that the error
  messages by system_printf() are displayed to screen reliably.
  This is needed when stdout is redirected to another pty. In this
  case, process has two ptys opened. However, process can attach
  to only one console. So it is necessary to change console attached.

winsup/cygwin/fhandler_tty.cc

@@ -88,16 +88,59 @@ set_switch_to_pcon (void)
       }
 }
 
+static void
+force_attach_to_pcon (HANDLE h)
+{
+  bool attach_done = false;
+  for (int n = 0; n < 2; n ++)
+    {
+      /* First time, attach to the pty whose handle value is match.
+	 Second time, try to attach to any pty. */
+      cygheap_fdenum cfd (false);
+      while (cfd.next () >= 0)
+	if (cfd->get_major () == DEV_PTYS_MAJOR)
+	  {
+	    fhandler_base *fh = cfd;
+	    fhandler_pty_slave *ptys = (fhandler_pty_slave *) fh;
+	    if (n != 0
+		|| h == ptys->get_handle ()
+		|| h == ptys->get_output_handle ())
+	      {
+		if (fhandler_console::get_console_process_id
+				  (ptys->getHelperProcessId (), true))
+		  attach_done = true;
+		else
+		  {
+		    FreeConsole ();
+		    if (AttachConsole (ptys->getHelperProcessId ()))
+		      {
+			pcon_attached_to = ptys->get_minor ();
+			attach_done = true;
+		      }
+		    else
+		      pcon_attached_to = -1;
+		  }
+		break;
+	      }
+	  }
+      if (attach_done)
+	break;
+    }
+}
+
 void
 set_ishybrid_and_switch_to_pcon (HANDLE h)
 {
-  DWORD dummy;
-  if (!isHybrid
-      && GetFileType (h) == FILE_TYPE_CHAR
-      && GetConsoleMode (h, &dummy))
+  if (GetFileType (h) == FILE_TYPE_CHAR)
     {
-      isHybrid = true;
-      set_switch_to_pcon ();
+      force_attach_to_pcon (h);
+      DWORD dummy;
+      if (!isHybrid && (GetConsoleMode (h, &dummy)
+			|| GetLastError () != ERROR_INVALID_HANDLE))
+	{
+	  isHybrid = true;
+	  set_switch_to_pcon ();
+	}
     }
 }