The thread list is used by the debugger to inspect running and stopped threads.

Needed for pthread_attr_*() (and in general to make sure the stack is
a regular vma as expected by the payload).

Thread timers can be set to wake a thread at a specified time, or cancelled.

Required by pthread_getattr_np(), in turn required by the jvm.

This way everyone's running on a similar sized stack.  Theoretically the
main thread can be destroyed as well.

Uniprocessor, non-preemptive, round-robin.