formatter: unblock storing fctx as a template resource
To keep templateformatter._renderitem() simple, a repo instance is looked
through ctx if available. This is probably good for future subrepo support
where ctx.repo() may be different from the global repo.
<Include>
<?if $(var.Platform) = "x64" ?>
<?define IsX64 = yes ?>
<?else?>
<?define IsX64 = no ?>
<?endif?>
</Include>