Make c10d tests -Werror clean (#69703)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/69703
Test Plan: Imported from OSS
Reviewed By: seemethere
Differential Revision: D32997001
Pulled By: malfet
fbshipit-source-id: 38b5f195c04f2b3b920e6883a96fe9a36345b9d2
