phabricator: switch to the creatediff endpoint
This lets the extension submit binary files, as well as set branch info so that
it is exposed in the Phabricator interface.
Differential Revision: https://phab.mercurial-scm.org/D7053
<Include>
<?if $(var.Platform) = "x64" ?>
<?define IsX64 = yes ?>
<?else?>
<?define IsX64 = no ?>
<?endif?>
</Include>