title: Virtual method but no virtual destructor
body: <p>I see warnings like this</p>
  <pre><code>destructor called on non-final 'some_class_type' that has virtual functions but non-virtual destructor
  </code></pre>
  <p>on gnu compilers, but on our internal continuous integration tests that also compiles with <code>clang</code>, this warning becomes an error.</p>
  <p>Is this supposed to happen, and if so, why does clang characterize this as an error, but gnu doesn't?</p>