Normally, I would try to fix problems rather than backing out of a commit. However, today it was not possible for me to give the problem any attention. Given the severity (it broke the build process), I decided to revert it so that I could look at in piece and quiet.
When the fix to ucs-normalize has been pushed, I will verify that Emacs builds from scratch with my patch is installed (on multiple systems), before publishing it again.
Anyway, I will post further messages on this to the "22169" issue, to avoid filling emacs-devel and personal mail boxes with (possibly) irrelevant information.
Finally, thanks to everybody reporting this.