timers: setImmediate v8 optimization fix

Prevent v8 disabling optimization for scenario "bad value context for
arguments value".

Solves #6631

Signed-off-by: Trevor Norris <trev.norris@gmail.com>

lib/timers.js

@@ -424,14 +424,16 @@ Immediate.prototype._idlePrev = undefined;
 
 exports.setImmediate = function(callback) {
   var immediate = new Immediate();
-  var args;
+  var args, index;
 
   L.init(immediate);
 
   immediate._onImmediate = callback;
 
   if (arguments.length > 1) {
-    args = Array.prototype.slice.call(arguments, 1);
+    args = [];
+    for (index = 1; index < arguments.length; index++)
+      args.push(arguments[index]);
 
     immediate._onImmediate = function() {
       callback.apply(immediate, args);