Fix op benchmark (#42757)
Summary:
A benchmark relies on abs_ having a functional variant.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42757
Reviewed By: ngimel
Differential Revision: D23011037
Pulled By: mruberry
fbshipit-source-id: c04866015fa259e4c544e5cf0c33ca1e11091d92
