[strong] Implement static restrictions on binding/assignment to 'undefined' identifier.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index e7e0938d56a8f6b117e10120ef029529e5f80062..68965ead2d5ebf1d1e500da9482c040491c7d705 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -166,6 +166,7 @@ var kMessages = {
   strict_caller:                 ["Illegal access to a strict mode caller function."],
   strong_ellision:               ["In strong mode, arrays with holes are deprecated, use maps instead"],
   strong_arguments:              ["In strong mode, 'arguments' is deprecated, use '...args' instead"],
+  strong_undefined:              ["In strong mode, binding or assigning to 'undefined' is deprecated"],
   strong_equal:                  ["In strong mode, '==' and '!=' are deprecated, use '===' and '!==' instead"],
   strong_delete:                 ["In strong mode, 'delete' is deprecated, use maps or sets instead"],
   strong_var:                    ["In strong mode, 'var' is deprecated, use 'let' or 'const' instead"],