build.rs

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::Path;

fn main() {
    let dest = env::var("OUT_DIR").unwrap();
    let mut file = File::create(&Path::new(&dest).join("ice.rs")).unwrap();

    writeln!(&mut file, "#[derive(Clone)] pub struct Little;").unwrap();
    writeln!(&mut file, "#[derive(Clone)] pub struct Big(").unwrap();

    for _ in 0..614 {
        writeln!(&mut file, "Little,").unwrap();
    }

    writeln!(&mut file, ");").unwrap();
}

lib.rs

include!(concat!(env!("OUT_DIR"), "/ice.rs"));