message: Move constexpr outside of another to simplify evaluation to work around compiler bug in xlc
diff: @@ -1571,12 +1571,10 @@ class format_arg_store
  friend class basic_format_args<Context>;
  + static constexpr unsigned long long type_encoding = detail::encode_types<Context, Args...>();
  static constexpr unsigned long long desc =
  - (is_packed ? detail::encode_types<Context, Args...>()
  - : detail::is_unpacked_bit | num_args) |
  - (num_named_args != 0
  - ? static_cast<unsigned long long>(detail::has_named_args_bit)
  - : 0);
  + (is_packed ? type_encoding : detail::is_unpacked_bit | num_args) |
  + (num_named_args != 0 ? static_cast<unsigned long long>(detail::has_named_args_bit) : 0);
  public:
  format_arg_store(const Args&... args)
  