[c10d] Add TCPSTore libuv backend support to c10d rendezvous. (#108284)
This enables libuv under env and tcp urls.
Under env either use the environment variable USE_LIBUV=1
or the url parameter use_lib=1.
Under tcp use the url parameter use_lib=1.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108284
Approved by: https://github.com/H-Huang, https://github.com/XilunWu
