C++ 17 structured binding support

Hi,

C++17 supports "structured bindings" . You can find the paper here: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0217r3.html

The example below works in C++17, but Qt Creator underlines the for line in red.

  std::map<int, std::string> test = {
    {1, "one"},
    {2, "two"},
    {3, "three"}
  };

  for (auto&& [key, value]: test)
  {
    std::cout << key << " " << value << std::endl;
  }

I could not test the clang code model as i had a custom clang version compiled without recompiling qtcreator for it's clang codemodel plugin.