rust/chg/build.rs

tests: show poor error message for  `hg cp -A --at-rev . non-existent dst`

Differential Revision: https://phab.mercurial-scm.org/D8495

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