Only minor changes are required to make the kernel 64 bit compatible.
Most of the changes are either DEBUG/printf formatting or different types for void pointer casting.
The only other change is the type of the `data` member in priority_queue_node_t, as `data` must be able to store a pointer.
For current architectures, the assumption `sizeof(unsigned int) == sizeof(void *)` holds, but not for 64 bit.
Therefore, the type is changed to `uintptr_t', which has the same size for the current architectures, but can also store a pointer in 64 bits.
