[turbofan] Improve typed lowering for JSToBoolean.

test/mjsunit/asm/do-while.js

+// Copyright 2014 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(stdlib, foreign, buffer) {
+  "use asm";
+  function f(i) {
+    var j;
+    i = i|0;
+    do {
+      if (i > 0) {
+        j = i != 0;
+        i = (i - 1) | 0;
+      } else {
+        j = 0;
+      }
+    } while (j);
+    return i;
+  }
+  return {f:f};
+}
+
+var m = Module(this, {}, new ArrayBuffer(64*1024));
+
+assertEquals(-1, m.f("-1"));
+assertEquals(0, m.f(-Math.infinity));
+assertEquals(0, m.f(undefined));
+assertEquals(0, m.f(0));
+assertEquals(0, m.f(1));
+assertEquals(0, m.f(100));