Disable unknown warning option error on Mac.
Clang 19 requires `-Wno-error=c23-extensions` (https://github.com/jax-ml/jax/commit/3d006e9f1566afc6e450243cd4dfdf792433a73d) but this flag is not supported
on Apple Clang in XCode 16.0 so we suppress unknown warning option errors on Mac CI builds.
Fixes https://btx.cloud.google.com/invocations/15ded1a8-956e-462e-9da9-9748b4e4a03e/targets/ml_oss%2Fjax%2Fbuild_artifacts%2Fnightly%2Fjaxlib%2Fmacos_arm64%2Fpy310/log
PiperOrigin-RevId: 747489006