contrib/wix/defines.wxi

githelp: format with %d if an integer

Python 3 doesn't allow us to format an int with %s like Python 2
did. So handle that.

Differential Revision: https://phab.mercurial-scm.org/D5726

<Include>

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

</Include>