rust/chg/build.rs

cext: restore the ability to build on Windows with py2

This broke in e92ca942ddca.

Differential Revision: https://phab.mercurial-scm.org/D9867

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