Compiled on RPI3B with 6.1.25-piCore-v7 with F2FS filesystem

Append this section to the bottom of Cargo.toml

[profile.release]
opt-level = "z"  # Optimize for size. "s" is a synonym (opt-level = "s")
lto = true
codegen-units = 1
panic = 'abort'
strip = true

Compile:
# default (first time, it need time to download certain files to the system, second round is faster if you messed up something for the first time)
time cargo build --release
real    33m 5.34s
user    39m 28.37s
sys     2m 2.22s

install -Dm755 target/release/cbindgen /tmp/packing-cbindgen/usr/local/bin/cbindgen