change ClassType::compilation_unit to return owning ptr (#21787)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21787
ghimport-source-id: eed7b98b0f02745066164b8ef3906291931e2ecb
Test Plan: Imported from OSS
Differential Revision: D15831353
Pulled By: suo
fbshipit-source-id: 50695c35dba8ffea710cbc9aca8aba6a75512fa0
