Codechange: [OSX] Prevent the compiler from using SSE4 instructions unless we want to. #8476
Motivation / Problem
Apple clang might default to use SSE4 instructions in the optimizer that don't work on old systems.
Tell the compiler to not use SSE4 in general, except for those files where we specifically want it.
We might loose a tiny fraction of performance on newer systems.
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.
…nless we want to. This improves compatibility on older systems. We don't need to disable anything older, as there are no SSE2-only Macs.