contrib/wix/defines.wxi

run-tests: unset CHGDEBUG

With CHGDEBUG, chg outputs much more stuff and the test could fail running
with --chg. So unset the environment variable.

<Include>

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

</Include>