message: Add colors to the error message.
diff: @@ -50,14 +50,23 @@ EmissionContext::EmissionContext(std::unique_ptr<HloModule> module)
  const string& instr_name, int indent,
  bool is_root) {
  const string tab(2 * indent, ' ');
  - string result =
  - absl::StrCat(tab, is_root ? "ROOT " : "", instr_name);
  if (!instructions_with_error.count(instr)) {
  - return result;
  + return absl::StrCat(tab, is_root ? "ROOT " : "",
  + instr_name);
  }
  + static constexpr char kStartBold[] = "\033[1m";
  + static constexpr char kStartRed[] = "\033[31m";
  + static constexpr char kBackToNormal[] = "\033[0m";
  +
  + string result =
  + absl::StrCat(tab, kStartBold, is_root ? "ROOT " : "",
  + instr_name, kBackToNormal);
  +
  for (const string& err : instructions_with_error.at(instr)) {
  - absl::SubstituteAndAppend(&result, "\n$0 FAILED: $1", tab,
  - err);
  + absl::SubstituteAndAppend(
  + &result, "\n$0 $1$2FAILED:$3 $4$5$6", tab, kStartBold,
  + kStartRed, kBackToNormal, kStartBold, err,
  + kBackToNormal);
  }
  return result;
  })
  