Port BCELoss to ATen to increase accuracy (#31365)
Summary:
Fixes issue https://github.com/pytorch/pytorch/issues/24933
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31365
Differential Revision: D19557712
Pulled By: ezyang
fbshipit-source-id: 3ae78c949b2f6c21b294d986d28e09daa9b0c526
