Add use of portPOINTER_SIZE_TYPE to tasks.c to facilitate the removal of warnings when the pointer size is less than 32 bits.

Source/tasks.c

@@ -473,7 +473,7 @@ tskTCB * pxNewTCB;
 		#if( portSTACK_GROWTH < 0 )
 		{
 			pxTopOfStack = pxNewTCB->pxStack + ( usStackDepth - ( unsigned short ) 1 );
-			pxTopOfStack = ( portSTACK_TYPE * ) ( ( ( unsigned long ) pxTopOfStack ) & ( ( unsigned long ) ~portBYTE_ALIGNMENT_MASK  ) );
+			pxTopOfStack = ( portSTACK_TYPE * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ( portPOINTER_SIZE_TYPE ) ~portBYTE_ALIGNMENT_MASK  ) );
 
 			/* Check the alignment of the calculated top of stack is correct. */
 			configASSERT( ( ( ( unsigned long ) pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );