add clang-format check to CI (#15543)
Summary:
Simple check that runs against your PR's changes and complains if running clang-format would have created a change. Does nothing when run against master, so it's "safe" to accept changes that fail this check and it won't break the build.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15543
Reviewed By: soumith
Differential Revision: D13552080
Pulled By: suo
fbshipit-source-id: 462a73894c16e7108806af7fa88440c377d4d0d2
