respect MAX_JOBS (#16641)
Summary:
We inadvertently switch the OSX build over to ninja on CI. It then fails to respect MAX_JOBS and hits the same scache deadlock bug, this makes the ninja build respect MAX_JOBS.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16641
Differential Revision: D13910751
Pulled By: zdevito
fbshipit-source-id: 61bec500539519b019b74421a13cd87fc1d86090
