title: _countof in stdlib broken: why?
body: <p>I have a weird problem. In a very simple example (<strong>it's c, not c++</strong>):</p>
  
  <pre><code>int test[3];
  auto n = _countof(test);
  </code></pre>
  
  <p>I have error E0304:</p>
  
  <blockquote>
    <p>Severity  Code    Description Project File    Line    Suppression State Error
    (active)  E0304   no instance of function template "__countof_helper"
    matches the argument
    list</p>
  </blockquote>
  
  <p>I was not having this with visual studio 15.6.7, it appeared with 15.7 update. Toolset was not explicitely changed, it's still:</p>
  
  <blockquote>
    <p>platform toolset: Visual Studio 2017 (v141)</p>
  </blockquote>
  
  <p>What is happening ? How can I solve this ?</p>