extract //c10/macros into its own package (#69994)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69994
ghstack-source-id: 145799968
Test Plan: Imported from OSS
Reviewed By: malfet
Differential Revision: D33141011
fbshipit-source-id: caa97448f922d7c12980bf01669c1b3ef5c1213b
