Fix conversions between System.Address and C.void_ptr, again
Use 'Mod to convert from C.unwind.Unwind_Sword to Unwind_Word instead of Ada.Unchecked_Conversion
Use System'To_Address
Use System.Storage_Elements for address arithmetic
Use System.Address_To_Named_Access_Conversions instead of Ada.Unchecked_Conversion, again
Improve the implementation unit System.Reference_Counting