Cross Compiling Rust lambdas for Netlify Functions is fairly straightforward using
channel = "stable"
components = ["rustfmt", "clippy"]
targets = ["x86_64-unknown-linux-musl"]
linker = "x86_64-linux-musl-gcc"
You will also need the following.
brew install FiloSottile/musl-cross/musl-cross
brew install gcc
ln -s /usr/local/bin/x86_64-linux-musl-gcc /usr/local/bin/musl-gcc
Or you could use ed25519-dalek which is rust-native and skips these problems.