[parser] disallow language mode directive in body of function with non-simple parameters

test/mjsunit/strong/destructuring.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Flags: --harmony-destructuring
 // Flags: --harmony-arrow-functions --strong-mode --allow-natives-syntax
 
 (function() {
-  function f({ x = function() { return []; } }) { "use strong"; return x(); }
+  var f = (function() {
+    "use strong";
+    return function f({ x = function() { return []; } }) { return x(); };
+  })();
   var a = f({ x: undefined });
   assertTrue(%IsStrong(a));
 
   // TODO(rossberg): Loading non-existent properties during destructuring should
   // not throw in strong mode.
   assertThrows(function() { f({}); }, TypeError);
 
   function weakf({ x = function() { return []; } }) { return x(); }
   a = weakf({});
   assertFalse(%IsStrong(a));
 
   function outerf() { return []; }
-  function f2({ x = outerf }) { "use strong"; return x(); }
+  var f2 = (function() {
+    "use strong";
+    return function f2({ x = outerf }) { return x(); };
+  })();
   a = f2({ x: undefined });
   assertFalse(%IsStrong(a));
 })();