reduce_scatter raises a RuntimeError

[garrett361]

Hello, cross posting from ipex #647: torch-ccl does not support torch.distributed.reduce_scatter, despite the claims in the docs.

For instance, in 2.1.300+xpu we have: https://github.com/intel/torch-ccl/blob/b9ce71371fdb11f980befaa9d49a36a3c2c6e82b/src/ProcessGroupCCL.cpp#L871-L877 where the TORCH_CHECK line raises a RuntimeError.

See the ipex ticket for more details and code to reproduce the error.