Limit MAX_JOBS to 18 for linux binary builds (#44168)
Summary:
Because those jobs are running in Docker2XLarge+ container that has 20 cores
Unfortunately `nproc` returns number of cores available on the host rather than number of cores available to container
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44168
Reviewed By: walterddr, ngimel
Differential Revision: D23539558
Pulled By: malfet
fbshipit-source-id: 3df858722e153a8fcbe8ef6370b1a9c1993ada5b
