The function pointer to the previously set deallocator.
Registers a deallocator that runs after the thread terminates. When the thread structure and stack are being allocated dynamically, the deallocator can be used to release the memory. The thread stack is not used to run the deallocator. The thread structure and thread stack end (stack base - stack size) pointer are provided as deallocator arguments.
2012/05/25 Matched the actual header.