Pend a yield in portPRE_TASK_DELETE_HOOK (#1132)

Pend a yield in portPRE_TASK_DELETE_HOOK (#1132)

When a task deletes itself, it calls portPRE_TASK_DELETE_HOOK which
translates to vPortCloseRunningThread on the Windows port.
vPortCloseRunningThread never returns and as a result,
taskYIELD_WITHIN_API in vTaskDelete does not get called. As a result,
the next task is not scheduled when configUSE_PREEMPTION is set to 0.

This change records that a yield is pending so that the next tick
interrupt switches out the task that was deleted.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>