contrib/wix/defines.wxi

pull: gather explicit bookmark pulls with bookmark updates

There is no reason to make them at different times. So we gather them. This is
the first step toward merging them.

<Include>

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

</Include>