title: GCC (in any version) equivalent of clang's __type_pack_element to get Nth element of template parameter pack
body: <p><a href="https://reviews.llvm.org/D15421" rel="noreferrer">https://reviews.llvm.org/D15421</a></p>
  
  <p>clang has <code>__type_pack_element</code> which allows efficient indexing of parameter packs in variadic templates.  Is there a GCC equivalent?</p>
  
  <p>I am not interested in using <code>tuple_element_t</code>.  I am looking for an alternative that is a compiler primitive</p>