Add logic to auto-fetch submodules (#53461)
Summary:
In setup.py add logic to:
- Get list of submodules from .gitmodules file
- Auto-fetch submodules if none of them has been fetched
In CI:
- Test this on non-docker capable OSes (Windows and Mac)
- Use shallow submodule checkouts whenever possible
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53461
Reviewed By: ezyang
Differential Revision: D26871119
Pulled By: malfet
fbshipit-source-id: 8b23d6a4fcf04446eac11446e0113819476ef6ea
