title: Function template parameter pack followed by template parameter and specialisation
body: <p>Can a template parameter pack used in the definition of a function template, be followed by another template parameter, when that parameter is only given its required default value, in the definition; and not the declaration? Consider the following example:</p>
  
  <pre><code>template &lt;typename ...Ts, typename T&gt;
  auto sz(Ts...);
  
  template &lt;typename ...Ts, typename T = int&gt;
  auto sz(Ts...) { return sizeof...(Ts); }
  </code></pre>
  
  <p>I find that GCC and Clang disagree on this (GCC gives a compilation error).</p>