rustc/library/stdarch/crates/assert-instr-macro/build.rs

use std::env;

fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    let opt_level = env::var("OPT_LEVEL")
        .ok()
        .and_then(|s| s.parse().ok())
        .unwrap_or(0);
    let profile = env::var("PROFILE").unwrap_or_default();
    if profile == "release" || opt_level >= 2 {
        println!("cargo:rustc-cfg=optimized");
    }
}