I was kindly pointed to https://bugzilla.suse.com/show_bug.cgi?id=1166605#c5 privately (thanks!), which explains that __builtin_strlen is not actually a "builtin" and relying on that without providing a strlen implementation is not correct (and in fact broken with GCC-10).
I'm updating the patch's description accordingly and will upload this to unstable.
pgpExDJ9Njld8.pgp
Description: OpenPGP digital signature
