Use Blocking Wait if both Blocking Wait and Async Error Handling Are Set (#47926)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47926
Given that we're soon enabling async error handling in PET, we should make the behavior explicit when users have set NCCL_BLOCKING_WAIT in their own code while also using PET. This PR essentially gives blocking wait precedence (for now). This way the blast radius of the PET change is smaller, while we continue working with blocking wait users and discussing whether moving to async error handling may be a good fit.
ghstack-source-id: 116553583
Test Plan: Simple FBL run/CI
Reviewed By: jiayisuse
Differential Revision: D24928149
fbshipit-source-id: d42c038ad44607feb3d46dd65925237c564ff7a3
