[es8] Throw SyntaxError when tail call expressions occur in non-strict mode.

test/mjsunit/es6/tail-call.js

Index: test/mjsunit/es6/tail-call.js
diff --git a/test/mjsunit/es6/tail-call.js b/test/mjsunit/es6/tail-call.js
index e07f453eefaebbd659f6eb00d31136b8cd59b73e..6ecf04f3d99414e61e19ebba6349f74c9d63d7a7 100644
--- a/test/mjsunit/es6/tail-call.js
+++ b/test/mjsunit/es6/tail-call.js
@@ -261,9 +261,8 @@ function f_153(expected_call_stack, a) {
   }
   %NeverOptimizeFunction(g);
 
-  var context = 10;
   function f(v) {
-    return g(context);
+    return g();
   }
   %SetForceInlineFlag(f);