CI Fix: restore MAX_JOBS variable (#16415)
Summary:
Restores a CI workaround (https://github.com/pytorch/pytorch/pull/7361) that got dropped with build_pytorch_libs.sh.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16415
Differential Revision: D13833092
Pulled By: zdevito
fbshipit-source-id: f78b60cafd8da945790dba28de373b8faf46e9f5
