[es6] Initial support for let/const bindings in sloppy mode

test/mjsunit/harmony/block-let-crankshaft-sloppy.js

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 // Flags: --allow-natives-syntax
-
-"use strict";
+// Flags: --no-legacy-const --harmony-sloppy
 
 // Check that the following functions are optimizable.
 var functions = [ f1, f2, f3, f4, f5, f6, f7, f8, f9, f10, f11, f12, f13, f14,
                   f15, f16, f17, f18, f19, f20, f21, f22, f23, f24, f25, f26,
                   f27, f28, f29, f30, f31, f32, f33];
 
 for (var i = 0; i < functions.length; ++i) {
   var func = functions[i];
   print("Testing:");
   print(func);
@@ skipping 434 matching lines @@
 }
 
 %OptimizeFunctionOnNextCall(f);
 %OptimizeFunctionOnNextCall(g);
 
 f(12);
 g(12);
 
 assertTrue(%GetOptimizationStatus(f) != 2);
 assertTrue(%GetOptimizationStatus(g) != 2);