message: Register the new branch op rewrite patterns in hlo to lhlo conversion
  for good measure.
diff: @@ -581,6 +581,9 @@ struct HloLegalizeToLhlo
  populateHLOToLHLOConversionPattern(&context, &converter, &patterns);
  populateFuncOpTypeConversionPattern(patterns, &context, converter);
  populateCallOpTypeConversionPattern(patterns, &context, converter);
  + populateBranchOpInterfaceAndReturnOpTypeConversionPattern(
  + patterns, &context, converter);
  +
  populateShapeStructuralTypeConversionsAndLegality(&context, converter,
  patterns, target);
  if (failed(applyPartialConversion(getOperation(), target,
  