librsvg2 issue on ppc64le

If you are using Fedora, keep an eye on bug 1756838 where an LLVM 8 codegen issue is suspected with ppc64le causing an apparently faulty assertion in librsvg2. Unfortunately, this library is heavily used by (at least) GNOME and Xfce, meaning the issue may well make your desktop environment unusable -- for example, my Blackbird with the faulty library couldn't open the Applications drawer without crashing gnome-shell. Unfortunately, reducing the codegen issue has not been trivial.

The faulty build is librsvg2-2.46.0-2. If you keep, or downgrade to, librsvg2-2.45.90-1, this version is unaffected because it was built with an earlier toolchain. At least for Fedora, there appear to be no ABI changes between 2.45.90 and 2.46.0 (thanks to Dan Horák for confirming this) and there are no known or at least visible security issues in the earlier version, so it is currently safe to stay there.

On Fedora, if you are on F30 and have not yet been affected, you may wish to consider putting exclude=librsvg2 into /etc/dnf/dnf.conf to inhibit updates to it until further notice. If you have been affected, you can attempt to downgrade to 2.45.90, though interestingly on my (unaffected) Talos II that has not updated to the bad version,

% strings /usr/lib64/librsvg-2.so.2.46.0 | fgrep 2.4 | grep fc
[...]
librsvg-2.so.2.46.0-2.45.90-1.fc30.ppc64le.debug

It is possible F31 may smooth this over with LLVM 9, which should arrive later this month, and doesn't appear to suffer from this problem.

This may not affect other distributions with older toolchains. If your distribution is also affected, please post in the comments.