Yes, sorry I remembered incorrectly.
The rust compiler claims to be i686 and the CPU is i686 too, but the rust compiler is using Pentium 4 only instructions so it doesn't actually work for i686.
Edit: I see from the sister post that it is actually llvm and not rust, so I'm half barking up the wrong tree. But somehow this is not an issue with gcc and friends.
Wikipedia seems to correlate: https://en.wikipedia.org/wiki/Pentium_Pro, as do discussions on CMOV: https://stackoverflow.com/a/4429563