in build.rs [14:30]
fn clang_args() -> Vec<String> {
use mozbuild::{config::BINDGEN_SYSTEM_FLAGS, TOPOBJDIR};
let mut flags: Vec<String> = BINDGEN_SYSTEM_FLAGS.iter().map(|s| s.to_string()).collect();
flags.push(String::from("-include"));
flags.push(
TOPOBJDIR
.join("dist")
.join("include")
.join("mozilla-config.h")
.to_str()
.unwrap()
.to_string(),
);
flags
}