contrib/packaging/wix/defines.wxi

dirstatemap: use the default code to handle "possibly_dirty" case

This case is quite simple too

Differential Revision: https://phab.mercurial-scm.org/D11324

<Include>

  <?if $(var.Platform) = "x64" ?>
    <?define IsX64 = yes ?>
  <?else?>
    <?define IsX64 = no ?>
  <?endif?>

</Include>