contrib/wix/defines.wxi

test: use generaldelta in 'test-rebase-conflict.t'

Doing this has some minor impacts on test output since the rebase
backup bundle moves to bundle2.

<Include>

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

</Include>