title: Missing include gives no compile error on RedHat 6
body: <p>This snippet can not be compiled, since <a href="https://en.cppreference.com/w/cpp/algorithm/accumulate" rel="nofollow noreferrer">std::accumulate</a> is found in the header <code>numeric</code>, which is not included.</p>
  
  <pre><code>#include &lt;algorithm&gt;
  #include &lt;vector&gt;
  
  int main () {
      std::vector&lt;int&gt; vec{ 1, 2, 3, 4 };
      return std::accumulate(vec.begin(), vec.end(),0);
  }
  </code></pre>
  
  <p>The <a href="https://gcc.godbolt.org/z/MW3DuY" rel="nofollow noreferrer">compiler explorer</a> gives me the correct error message</p>
  
  <pre><code>&lt;source&gt;(6): error: namespace "std" has no member "accumulate"
        return std::accumulate(vec.begin(), vec.end(),0);
  </code></pre>
  
  <p>I am using RedHat 6 and the intel compiler version 18.0.3. If I compile it with this setting, I get no error and the result is fine. No warning is shown, even if <code>-Wall</code> is used. </p>
  
  <p>My question is, why don't I get an appropriate error message?</p>