Native backend produces incorrect code with LLVM 8... but only on MacOS?

This is bound to be a fun one: one of my larger kernels is producing incorrect results when compiled with accelerate-llvm-native on MacOS when using LLVM 8. The same kernel agrees with the interpreter on all my Linux machines, and also agrees with the interpreter on my Mac when I use LLVM 7.

I've got two working theories:

- I think the only platform-specific part of accelerate-llvm-native is the linker, so perhaps there's some problem there? Although I can't imagine what LLVM would break from 7 to 8 that would cause a linker to do the wrong thing...
- My Mac is a 2018 MBP with an Intel i9. All the Linux machines I've tested on have i7s. The problem kernel does a huge number of floating point ops, so perhaps some optimization LLVM 8 is doing changes the numerical stability in a way that doesn't matter on an i7, but does matter on an i9? That certainly wouldn't be the weirdest numerical stability issue I've run in to...

Once I've got a few spare hours I'll begin pruning down a minimal repro.