Summary:
**Summary**
This commit adds a script that fetches a platform-appropriate `clang-format` binary
from S3 for use during PyTorch development. The goal is for everyone to use the exact
same `clang-format` binary so that there are no formatting conflicts.
**Testing**
Ran the script.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33644
Differential Revision: D20076598
Pulled By: SplitInfinity
fbshipit-source-id: cd837076fd30e9c7a8280665c0d652a33b559047
