extract //c10/macros to its own package (#70849)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70849
ghstack-source-id: 146960563
Test Plan: Bazel CI tests will protect this.
Reviewed By: malfet
Differential Revision: D33297235
fbshipit-source-id: 6504a977e82ad2f2232a74233b96cdea8bf94a20
