`Hardware::CPU.ssse3` doesn't cover it fwiw, as the value is reported as true for my non Haswell system as well as the affected systems so it doesn't buy us anything.  So essentially we have to either blanket apply this to Haswell CPUs, or narrow it to extmodel 4.  Anything else just isn't going to catch it.

I agree that this will be resolved upstream once the official patches come through, so it's only a temporary issue for Homebrew anyway.  I have clearly documented the things that will need to change once the changes are merged upstream, and I will be keeping a close eye on the status at the Qt end and so will be prepared and willing when they make the drop.