[llvm] Constant Fold Logf128 calls (PR #84501)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

> This approach relies on unit tests, as more commonplace Clang/C tests and opt/llc/IR tests are not applicable since they are ignorant to the result of the compile time CMake check.

You can write code in lit.cfg.py to add a feature to config.available_features, then check for it using a REQUIRES clause.

https://github.com/llvm/llvm-project/pull/84501