[Foundation] Workaround for importer NS_REFINED_FOR_SWIFT failure in development environments

This is just a work-around for the underlying importer failure tracked by <rdar://problem/26921178>

Author: phausler

stdlib/public/SDK/Foundation/Foundation.swift

@@ -1217,14 +1217,7 @@ extension NSCoder {
 
   @nonobjc
   public func decodeObjectOfClasses(_ classes: NSSet?, forKey key: String) -> AnyObject? {
-    var classesAsNSObjects: Set<NSObject>? = nil
-    if let theClasses = classes {
-      classesAsNSObjects =
-        Set(IteratorSequence(NSFastEnumerationIterator(theClasses)).map {
-          unsafeBitCast($0, to: NSObject.self)
-        })
-    }
-    return self.__decodeObject(ofClasses: classesAsNSObjects, forKey: key)
+    return NS_Swift_NSCoder_decodeObjectOfClassesForKey(self as AnyObject, classes, key as AnyObject, nil)
   }
 
   @available(OSX 10.11, iOS 9.0, *)