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/serde_json
    
    the code of the file until where you have to start completion: use std::env;
use std::process::Command;
use std::str::{self, FromStr};

fn main() {
    // Decide ideal limb width for arithmetic in the float parser. Refer to
    // src/lexical/math.rs for where this has an effect.
    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
    match target_arch.as_str() {
        "aarch64" | "mips64" | "powerpc64" | "x86_64" => {
       
    
fn main() {
    // Decide ideal limb width for arithmetic in the float parser. Refer to
    // src/lexical/math.rs for where this has an effect.
    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
    match target_arch.as_str() {
        "aarch64" | "mips64" | "powerpc64" | "x86_64" => {
            println!("cargo:rustc-cfg=limb_width_64");
        }
        _ => {
            println!("cargo:rustc-cfg=limb_width_32");
        }
    }

    let minor = match rustc_minor_version() {
        Some(minor) => minor,
        None => return,
    };

    // BTreeMap::get_key_value
    // https://blog.rust-lang.org/2019/12/19/Rust-1.40.0.html#additions-to-the-standard-library
    if minor < 40 {
        println!("cargo:rustc-cfg=no_btreemap_get_key_value");
    }

    // BTreeMap::remove_entry
    // https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html#library-changes
    if minor < 45 {
        println!("cargo:rustc-cfg=no_btreemap_remove_entry");
    }
}