Rerun compilation if env changed

[segeljakt]

Hi, thank you for this cool crate. It works well but I have one problem. Cargo seems to cache compilation and not recompile when the environment variables change. Is it possible to add some similar functionality to:

// build.rs
println!("cargo:rerun-if-env-changed=FOO");

[EkardNT]

I've published a new 0.1.3 version to crates.io which has a tracked feature you can use to achieve this. This will be a nightly-only feature until rust-lang/rust#74690 is merged.