Update ATen internals to use int64_t for dimension indexing (#16739)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16739
Some code ATen locations seemed to use int, etc. inclorrectly where either
int64_t or size_t was required. Update them to use int64_t for dimension indexing where necessary.
Reviewed By: ezyang
Differential Revision: D13950124
fbshipit-source-id: aaf1cef783bf3c657aa03490f2616c35c816679f
