Support system-provided Intel TBB (#61934)
Summary:
This PR: (1) enables the use of a system-provided Intel TBB for building PyTorch, (2) removes `tbb:task_scheduler_init` references since it has been removed from TBB a while ago (3) marks the implementation of `_internal_set_num_threads` with a TODO as it requires a revision that fixes its thread allocation logic.
Tested with `test/run_test`; no new tests are introduced since there are no behavioral changes (removal of `tbb::task_scheduler_init` has no impact on the runtime behavior).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61934
Reviewed By: malfet
Differential Revision: D29805416
Pulled By: cbalioglu
fbshipit-source-id: 22042b428b57b8fede9dfcc83878d679a19561dd
