Comment on why Windows build_pytorch.bat builds twice (#22363)
Summary:
I've noticed that Windows CI seems to build twice, e.g., https://ci.pytorch.org/jenkins/job/pytorch-builds/job/pytorch-win-ws2016-cuda9-cudnn7-py3-build/60304/console
This adds a comment explaining why.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22363
Differential Revision: D16073609
Pulled By: zou3519
fbshipit-source-id: ddb422b7c7e18cc436caff2c5838373a82f69429
