skip_line function is wrong

[sunshaoce]

static Token *skip_line(Token *tok) {
  if (tok->at_bol)
    return tok;
  warn_tok(tok, "extra token");
  while (tok->at_bol)
    tok = tok->next;
  return tok;
}

while (tok->at_bol)should bewhile (!tok->at_bol)

static Token *skip_line(Token *tok) {
  if (tok->at_bol)
    return tok;
  warn_tok(tok, "extra token");
  while (!tok->at_bol)
    tok = tok->next;
  return tok;
}