Cygwin: pty: Attach to stub process when non-cygwin app inherits pcon.

- If two non-cygwin apps are started simultaneously, attaching to
  pseudo console sometimes fails. This is because the second app
  trys to attach to the process not started yet. This patch avoids
  the issue by attaching to the stub process rather than the other
  non-cygwin app.

winsup/cygwin/fhandler_tty.cc

@@ -3104,7 +3104,7 @@ fhandler_pty_slave::setup_pseudoconsole (bool nopcon)
 		       0, TRUE, DUPLICATE_SAME_ACCESS);
       CloseHandle (pcon_owner);
       FreeConsole ();
-      AttachConsole (p->dwProcessId);
+      AttachConsole (p->exec_dwProcessId);
       goto skip_create;
     }