call find_package(OpenMP) only when USE_OPENMP=ON (#30223)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30223
I ran into find_package(OpenMP) failure in some linux environment when
USE_OPENMP=OFF. Figured this workaround to unblock - not sure how hard
to find & fix the root cause of find_package() failure.
Test:
- works in my case;
- will check CI;
Test Plan: Imported from OSS
Differential Revision: D18640309
Pulled By: ljk53
fbshipit-source-id: b5b30623f5da4edbe59574a8b35286b74c3225d3
