added stack allocation fields to the cpu table

c/src/exec/score/cpu/i386/cpu.h

@@ -104,6 +104,9 @@ typedef struct {
   boolean      do_zero_of_workspace;
   unsigned32   interrupt_stack_size;
   unsigned32   extra_mpci_receive_server_stack;
+  void *     (*stack_allocate_hook)( unsigned32 );
+  void       (*stack_free_hook)( void* );
+  /* end of fields required on all CPUs */
 
   unsigned32   interrupt_table_segment;
   void        *interrupt_table_offset;