message: Run optimizers even if we can't detect the CPU device: constant folding will
  create its own cpu device, and the other optimizers don't need a cpu device.
diff: @@ -348,10 +348,6 @@ Status GraphExecutionState::OptimizeGraph(
  cpu_device = device;
  }
  }
  - if (cpu_device == nullptr) {
  - return errors::Internal(
  - "Unable to find CPU device needed for constant folding");
  - }
  grappler::VirtualCluster cluster(device_map);
  GraphDef new_graph;
  TF_RETURN_IF_ERROR(grappler::RunMetaOptimizer(
  