vhdl-mode: don't use timer accessors in XEmacs

* lisp/progmodes/vhdl-mode.el (vhdl-run-when-idle):
No need to activate a newly created idle timer; keep it as
compatibility (or voodoo) code for XEmacs which probably doesn't have
the timer accessors anyway.

lisp/progmodes/vhdl-mode.el

@@ -2341,7 +2341,8 @@ Ignore byte-compiler warnings you might see."
   (if (fboundp 'start-itimer)
       (start-itimer "vhdl-mode" function secs repeat t)
     ;; explicitly activate timer (necessary when Emacs is already idle)
-    (setf (timer--triggered (run-with-idle-timer secs repeat function)) nil)))
+    (when (featurep 'xemacs)
+      (aset (run-with-idle-timer secs repeat function) 0 nil))))
 
 (defun vhdl-warning-when-idle (&rest args)
   "Wait until idle, then print out warning STRING and beep."