am trying to fix problems when targeting 16bit system <https://github.com/nim-lang/Nim/pull/20829>
the first problem comes to me is the algorithm in `lib/system/alloc.nim` cause overflow,I guess it assumign the `sizeof(int) > 2` after tweaked `wide string` implementation cause overflow, I googled found <https://docwiki.embarcadero.com/RADStudio/Sydney/en/String_Types_(Delphi)> Delphi has limit internal string implementation support for mobile platform. hope someone can give me some guidances, thanks!
