- fish 4.0.0 / Rust: (cargo build): 16 seconds

- fish 4.0.0 / Rust: (cargo build --release): 37 seconds

- fish 3.7.1 / C++: cmake ..: 10 seconds + make -j8: 13 seconds = 23 seconds

So yeah, C++ was slightly faster in release mode, but slower in non-release. I'd say this is yet another win for Rust, frankly.