C++20 can not construct a std::string with a UTF-8 encoded string literal

[Ignition]

Problem is in this file

std::vector\<std::string> <lexer.name>::_ruleNames = {
  <lexer.ruleNames: {r | u8"<r>"}; separator = ", ", wrap, anchor>
};

In C++20 this is ill formed, see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1423r2.html for more details.