SMP: preemptionPoint() should know about other cores

[Indanz]

To limit WCET, preemptionPoint() is called to check if there is anything else to do. It returns EXCEPTION_PREEMPTED when IRQs are pending or when the current task runs out of budget.

But with SMP, the global kernel lock will be held and other cpu cores can be blocked on the lock. preemptionPoint() either needs to check for other cores wanting to take the lock, or to always return EXCEPTION_PREEMPTED on SMP.

This issue was raised on the mailing list by Yadong Li.