use std::env;use std::fs;use std::io::Write;use std::path;fn main() {    println!("cargo:rerun-if-changed=build.rs");    // env::ARCH doesn't include the full triplet, and as far as I know there isn't a cleaner way of getting the full triplet    // (see cargo.rs for the rest of this implementation)    let out = path::PathBuf::from(env::var_os("OUT_DIR").expect("run within cargo"))        .join("current_target.txt");    let default_target = env::var("TARGET").expect("run as cargo build script");    let mut file = fs::File::create(out).expect("can write to OUT_DIR");    file.write_all(default_target.as_bytes())        .expect("can write to OUT_DIR");}