add test for number of jobs when building (#65162)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/65162
Test Plan: Imported from OSS
Reviewed By: driazati
Differential Revision: D30998006
Pulled By: dagitses
fbshipit-source-id: 8b8d45668acf0e6c0f16df0f705a1af8c6d4f22d
