Context: A few days ago Arch pushed out a legitimately broken update. This was because they shipped out a testing version of util-linux. They very quickly fixed this... except I use SE Linux (say what you will I wanted to dive into it) and now I'm stuck waiting for the maintainer to update the AUR package so I can fix my system. This is not a general arch problem but a me problem because of my less standard, more niche build. Although the wait is genuinely making me reconsider using SE Linux as it's been a hassle to maintain (just to keep things up to date, I gave up on keeping it in enforcing mode).
I attempted to do so, but the package applies some patches to the source code and it's version dependent. I don't have the experience with this specific project to easily fix it, and I suspect by the time I figure it out the update will have already been pushed.
You can try rolling back to a previous version though.
By checking the log section in the AUR,
you can see all the commits (changes) done to the build files.
https://aur.archlinux.org/cgit/aur.git/log/?h=util-linux-selinux
Clicking on a commit message shows you the diff.
Start by the last commit,
undo the changes (green lines),
re-apply the removals (red lines),
then attempt to re-build.
If that did not work out,
do the same for the commit before that until you rolled back up to the latest working version.