I'm so proud of this build file.

build.rs

extern crate bindgen;
extern crate cmake;
extern crate filetime;

use std::env;
use std::fs;
use filetime::FileTime;

fn generate_bindings(out_dir: &str) {
    let ode_dir = format!("{}/build", out_dir);
    let bindings = bindgen::Builder::default()
        .header("ode/include/ode/ode.h")
        .clang_arg("-I./ode/include")
        .clang_arg(format!("-I{}/include", ode_dir))
        .blacklist_type("_bindgen_ty_1")
        .blacklist_type("max_align_t")
        .generate()
        .expect("Unable to generate bindings");

    bindings.write_to_file(format!("{}/ffi.rs", out_dir))
        .expect("Couldn't write file");
}

fn compile_cmake() {
    cmake::Config::new("ode")
        .build_target("")
        .build();
}

fn exec_if_newer(inpath: &str, outpath: &str, build: &Fn()) {
    match fs::metadata(outpath) {
        Ok(metadata) => {
            let outtime = FileTime::from_last_modification_time(&metadata);
            let intime = FileTime::from_last_modification_time(&fs::metadata(inpath)
                                                               .expect(&format!("Path {} not found", inpath)));
            if outtime < intime {
                build();
            }
        },
        _ => { build(); }
    }
}

fn main() {
    let out_dir = env::var("OUT_DIR").unwrap();

    exec_if_newer("ode", &format!("{}/build", out_dir), &compile_cmake);

    exec_if_newer("ode", &format!("{}/ffi.rs", out_dir), &|| generate_bindings(&out_dir));

	println!("cargo:rustc-link-search={}/build", out_dir);
	println!("cargo:rustc-link-lib=ode");
}