You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: build.rs
    path of file: ./repos/phaser/phaser/vendor/futures-core
    
    the code of the file until where you have to start completion: #![warn(rust_2018_idioms, single_use_lifetimes)]

use st
    
fn main() {
    let target = match env::var("TARGET") {
        Ok(target) => target,
        Err(e) => {
            println!(
                "cargo:warning={}: unable to get TARGET environment variable: {}",
                env!("CARGO_PKG_NAME"),
                e
            );
            return;
        }
    };

    // Note that this is `no_*`, not `has_*`. This allows treating
    // `cfg(target_has_atomic = "ptr")` as true when the build script doesn't
    // run. This is needed for compatibility with non-cargo build systems that
    // don't run the build script.
    if NO_ATOMIC_CAS_TARGETS.contains(&&*target) {
        println!("cargo:rustc-cfg=futures_no_atomic_cas");
    }

    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
}