6a9a1c40d1
With cmake now found, Homebrew's CMake 4 refuses the vendored libopus's
`cmake_minimum_required(VERSION <3.5)` ("Compatibility with CMake < 3.5 has been
removed"). Export CMAKE_POLICY_VERSION_MINIMUM=3.5 (the same knob the Windows
build uses) so the cmake crate's child cmake configures the audiopus_sys libopus.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>