Ah, now I understand. This change is necessary to fix the build after https://reviews.llvm.org/D92044. The problem is that CI didn't run for that revision, so we didn't catch the failure. When you submit a patch, please make sure to follow the arc diff instructions here: https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-command-line.
Using arc diff makes sure that the right repository is populated in the Phabricator revision, and that allows CI to run. I know it's easy to miss (and would love for a more robust setup), but that's what we have for now. :-) I'll check this in now.