cmake-rs hardcodes opt_level(0) and replaces CMake's Release C flags, so
ggml/whisper.cpp compiled at /Od — root cause of the W1 CPU-pathology
(RTF ~20) in docs/benchmarks/2026-07-parakeet-vs-whisper.md. cc-rs appends
env CFLAGS/CXXFLAGS last, restoring optimization for all native deps.