[turbofan] Don't eliminate unused CheckFloat64Hole.

test/mjsunit/regress/regress-crbug-686737.js

+// Copyright 2017 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
+
+Object.prototype.__defineGetter__(0, () => { throw Error() });
+var a = [,0.1];
+function foo(i) { a[i]; }
+foo(1);
+foo(1);
+%OptimizeFunctionOnNextCall(foo);
+assertThrows(() => foo(0), Error);