fix bug in arm64 marking garbage collector, fix marking of strings in mark...

fix bug in arm64 marking garbage collector, fix marking of strings in mark using pointer reversal (2 constants were incorrect, only one was fixed by the previous commit)

arm64mark.s

@@ -2047,7 +2047,7 @@ __mark__strict__bool__array:
 
 __mark_string_:
 	ldr	x4,[x8,#8]
-	add	x4,x4,#16+3
+	add	x4,x4,#16+7
 	lsr	x4,x4,#3
 
 __mark_basic_array: