[crankshaft] Fixing ES6 tail call elimination.

test/mjsunit/es6/tail-call-megatest.js

 // Copyright 2016 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: --allow-natives-syntax --harmony-tailcalls
-// TODO(v8:4698), TODO(ishell): support these cases.
-// Flags: --turbo --nostress-opt
 
 
 Error.prepareStackTrace = (error,stack) => {
   error.strace = stack;
   return error.message + "\n    at " + stack.join("\n    at ");
 }
 
 
 function checkStackTrace(expected) {
   var e = new Error();
@@ skipping 342 matching lines @@
             });
           });
         });
       });
     });
   });
 }
 
 // Uncomment to run all the tests at once or use shard runners.
 //run_tests();