rust/chg/build.rs

rust: populate mmap by default if available

See 522b4d729e89edc76544fa549ed36de4aea0b7fb for more details.

Background population to follow in a later patch.

fn main() {
    cc::Build::new()
        .warnings(true)
        .file("src/sendfds.c")
        .file("src/sighandlers.c")
        .compile("procutil");
}