Is there an easy way to unbrick a system affected by the issue? such as a kernel-line option or a configuration file in /etc? I don't see how I can set a GLIBC_TUNABLES environment variable for the whole system.
I was trying during my testing to set such option globally somehow, but failed, though maybe some method for this exists. As it stands I only see two possibilities of unbricking a system, both assuming you can access the partition externally from some bootable system:
1. Downgrade the affected libc6 package to a version before the one causing issues (either chroot and dpkg, or just extract and physically replace the files), after booting apt-mark hold libc6 to prevent faulty update from being installed until the issue is fixed
2. Or install intel-microcode package, assuming the microcode update adds the missing instructions in particular case, basically coincidentally fixing this issue (the updated CPU microcode is loaded on every bootup)