Method skip_until

ppcc/src/parser.cc:75–80

    return source->filename->ends_with(".c");
  }
  void skip_until(Word64 syms) {
    syms |= BIT(SymEOF);
    while (!TEST(syms, input->at(pos).sym)) {
      pos++;
    }
  }
  void skip_while(Word64 syms) {
    while (TEST(syms, input->at(pos).sym)) {
      pos++;