message: Fix build on MSVC 14.11.25503
diff: @@ -161,7 +161,7 @@ auto config_option_set::parse(config_map& config, argument_iterator first,
  if (i->compare(0, 2, "--") == 0) {
  // Long options use the syntax "--<name>=<value>" and consume only a
  // single argument.
  - static constexpr auto npos = std::string::npos;
  + auto npos = std::string::npos;
  auto assign_op = i->find('=');
  auto name = assign_op == npos ? i->substr(2)
  : i->substr(2, assign_op - 2);
  