message: [Assembler] Elaborate directive error message
diff: @@ -87,6 +87,9 @@ protected:
  const auto& directive = line.tokens.at(0);
  if (m_directivesMap.count(directive) == 0) {
  + if (directive.startsWith(".")) {
  + return {Error(line.sourceLine, "Unknown directive '" + directive + "'")};
  + }
  ok = false;
  // Not a directive
  return std::nullopt;
  