Make use of our S3 mirror if Yann Lecunn's website is not accessible (#34215)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34215
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D20251538
Pulled By: ezyang
fbshipit-source-id: c419f0ce869aca4dede7e37ebd274a08632d10bf
