[inductor] Disable parallel compilation inside fbcode (#89926)
Forking python processes using `multiprocessing` doesn't play nicely
with certain aspects of FB infra, so let's disable it until we find a better
solution.
Differential Revision: [D41618774](https://our.internmc.facebook.com/intern/diff/D41618774/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89926
Approved by: https://github.com/desertfire
