Build torch.distributed with Gloo backend on macOS (#25260)
Summary:
In facebookincubator/gloo#212, a libuv based Gloo transport was introduced,
which allows us to use Gloo on macOS (and later perhaps also Windows). This
commit updates CMake code to enable building with USE_DISTRIBUTED=1 on macOS.
A few notes:
* The Caffe2 ops are not compiled, for they depend on `gloo::transport::tcp`.
* The process group implementation uses `gloo::transport::tcp` on Linux (because of `epoll(2)` on Linux and `gloo::transport::uv` on macOS).
* The TCP store works but sometimes crashes on process termination.
* The distributed tests are not yet run.
* The nightly builds don't use `USE_DISTRIBUTED=1`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25260
Reviewed By: mrshenli
Differential Revision: D17202381
Pulled By: pietern
fbshipit-source-id: ca80a82e78a05b4154271d2fb0ed31c8d9f26a7c
