test_reduce_sum_negative_axes_keepdims_exampleonnx->torch->linalg fails

[renxida]

A couple of lit tests:

• test_reduce_sum_negative_axes_keepdims_example
• test_reduce_sum_keepdims_example

fail to lower to linalg because:

Trying to match "(anonymous namespace)::ConvertReductionOp"
** Failure : dim argument must be a constant int list or None

https://github.com/llvm/torch-mlir/blob/3c252cdd44f411ef67e3a759319be53b46396d44/lib/Conversion/TorchToLinalg/Reduction.cpp#L453

[renxida]

Looks like the static shape requirement goes pretty deep through Reduction.cpp and Utils.cpp. Probably not worth it at the moment to try to support dynamic shapes. Will make the shapes static in the test cases.