score: Introduce Thread_Entry_information

This avoids potential dead code in _Thread_Handler().  It gets rid of
the dangerous function pointer casts.

Update #2514.

cpukit/sapi/include/rtems/config.h

@@ -181,7 +181,7 @@ typedef struct {
    * This element points to the BSP's optional idle task which may override
    * the default one provided with RTEMS.
    */
-  Thread                       (*idle_task)( uintptr_t );
+  void                        *(*idle_task)( uintptr_t );
 
   /** 
    * This field specifies the size of the IDLE task's stack.  If less than or