Function ThreadSuspendSleep

Unlike suspending all threads where we can wait to acquire the mutator_lock_, suspending an individual thread requires polling. delay_us is the requested sleep wait. If delay_us is 0 then we use sched_yield instead of calling usleep. Although there is the possibility, here and elsewhere, that usleep could return -1 and errno = EINTR, there should be no problem if interrupted, so we do not check.