[turbofan] Fix control reducer with re-reducing branches.

test/mjsunit/regress/regress-458876.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.
+
+function module() {
+    "use asm";
+    function foo() {
+      do ; while (foo ? 0 : 1) ;
+      return -1 > 0 ? -1 : 0;
+    }
+    return foo;
+}
+
+var foo = module();
+assertEquals(0, foo());
+assertEquals(0, foo());