message: [XLA:GPU] Emit fused reduces from batchnorm expander
  This is an intermediate step until we have working multi-output fusion. Once
  we have it, this change should be reverted as it might interfere with fusion.
diff: @@ -157,11 +157,13 @@ Status OptimizeHloModule(HloModule* hlo_module, se::StreamExecutor* stream_exec,
  if (hlo_module->config().debug_options().xla_gpu_use_cudnn_batchnorm()) {
  pass.AddPass<CudnnBatchNormRewriter>();
  }
  + // TODO(kramerb): Remove use_fusion once instruction fusion can create
  + // multi-output fusions from the unfused expander output.
  pass.AddPass<BatchNormExpander>(
  /*rewrite_training_op=*/true,
  /*rewrite_inference_op=*/true,
  /*rewrite_grad_op=*/true,
  - /*use_fusion=*/false);
  + /*use_fusion=*/true);
  // Rewrite gather ops into smaller ones.
  pass.AddPass<GatherExpander>();
  