adjustlinkrev: handle 'None' value as source
When the source rev value is 'None', the ctx is a working context. We
cannot compute the ancestors from there so we directly skip to its
parents. This will be necessary to allow 'None' value for
'_descendantrev' itself necessary to make all contexts used in
'mergecopies' reuse the same '_ancestrycontext'.
<Include>
<?if $(var.Platform) = "x64" ?>
<?define IsX64 = yes ?>
<?else?>
<?define IsX64 = no ?>
<?endif?>
</Include>