[turbofan] Respect effect input when lowering JSToBoolean for string inputs.

test/mjsunit/regress/regress-4493-1.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: --allow-natives-syntax
 
-function foo(x) {
-  if (x === undefined) return;
-  while (true) {
-    while (1 || 2) { }
-    f();
-  }
-}
+function baz(x, f) { return x.length; };
+
+function bar(x, y) {
+  if (y) {}
+  baz(x, function() { return x; });
+};
+
+function foo(x) { bar(x, ''); }
 %OptimizeFunctionOnNextCall(foo);
-foo();
+foo(['a']);