[llvm] [Analysis] Guard logf128 cst folding (PR #106543)

[Matthew Devereau via llvm-commits]

https://github.com/MDevereau approved this pull request.

I've left a comment on [https://github.com/llvm/llvm-project/pull/104929/](https://github.com/llvm/llvm-project/pull/104929/) about planning to use an opt-out cmake define. I'm happy for this change to go upstream before that potentially happens though.

https://github.com/llvm/llvm-project/pull/106543