Add 64-bit indexing support to THC index reductions (#33405)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/32863, (together with https://github.com/pytorch/pytorch/issues/33310 for the `TensorIterator` reductions)
This adds 64-bit indexed kernels for `THC_reduceDimIndex` and uses `THCTensor_canUse32BitIndexMath` to switch between the two at runtime.
I have a test for this locally but haven't included it here because `max` is much slower than `argmax`. To the point where the test takes several minutes to call max on just one `2**32` element tensor. That seems excessive, even for a slow test but I can push it if preferred.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33405
Differential Revision: D20010769
Pulled By: ezyang
fbshipit-source-id: a8a86f662598d5fade4d90448436418422c699a3
