The cmake crate strips -O*/O* from CFLAGS and, with no explicit generator
on MSVC, overwrites CMAKE_C_FLAGS_RELEASE — so the previous CFLAGS=/O2
attempt could never work (verified: /DNDEBUG survived, /O2 stripped).
With CMAKE_GENERATOR=Ninja the override branch is skipped and CMake's
default Release flags (/O2 /Ob2 /DNDEBUG) reach ggml.
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.
iamdoubz