Bump up NCCL to 2.7.8 (#45251)
Summary:
Use latest NCCL
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45251
Reviewed By: mingzhe09088
Differential Revision: D23893064
Pulled By: mrshenli
fbshipit-source-id: 820dd166039e61a5aa59b4c5bbc615a7b18be8c3
