This is intended to reflect the POSIX sched_setparam API, which has some
cryptic language
(https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_08_04_01
) that as far as I can tell implies we should prioritize process
scheduling policies over thread scheduling policies. Technically this
means that a process must have its own sets of policies that are
considered first by the scheduler, but it seems unlikely anyone relies
on this behavior in practice. So we just override all thread's policies,
making them (at least before calls to pthread_setschedparam) behave
exactly like specified on the surface.
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