message: Remove linux compiler warnings
diff: @@ -120,7 +120,7 @@ public:
  num_outputs = 1;
  }
  - for (int64 i=0; i<num_outputs; i++) {
  + for (size_t i=0; i<num_outputs; i++) {
  poplar::Tensor out;
  TF_ASSIGN_OR_RETURN(out, FindInstructionOutput(tensor_map, inst, i));
  graph_->createHostRead(sep::GetCopyHandle(i), out);
  @@ -137,7 +137,7 @@ public:
  // For each output, see if there is an identical input and put it into the map
  const HloComputation* comp = inst->parent();
  - for (int64 o=0; o<num_outputs; o++) {
  + for (size_t o=0; o<num_outputs; o++) {
  poplar::Tensor out;
  TF_ASSIGN_OR_RETURN(out, FindInstructionOutput(tensor_map, inst, o));
  @@ -161,7 +161,7 @@ public:
  }
  if (ShapeUtil::IsTuple(inst->shape())) {
  - for (int64 o=0; o<num_outputs; o++) {
  + for (size_t o=0; o<num_outputs; o++) {
  output_convertors[o] = GetOutputConversionFunction(
  ShapeUtil::GetTupleElementShape(inst->shape(), o));
  }
  