NCCL must depend on librt (#41978)
Summary:
Since NCCL makes calls to shm_open/shm_close it must depend on librt on Linux
This should fix `DSO missing from command line` error on some platforms
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41978
Reviewed By: colesbury
Differential Revision: D22721430
Pulled By: malfet
fbshipit-source-id: d2ae08ce9da3979daaae599e677d5e4519b080f0
