[Inductor] Limit the number of compile threads to the available cpu cores (#89377)
`config.compile_threads` gets the number of compile threads via `min(32,os.cpu_count())` while `os.cpu_count()` is the total number of cpu cores in the system, not the available ones. This would cause compile thread contention when the available cpu cores are less than `min(32,os.cpu_count())`, e.g., available cpu cores are limited with numactl or taskset, making the compilation very slow. This PR tries to use `len(os.sched_getaffinity(0))` if `os.sched_getaffinity` is available which returns the available number of cpu cores.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89377
Approved by: https://github.com/soumith
