rust/chg/build.rs

run-tests: extract a `process_cmd_line` from the main function

The main function doing line comparison is quite complex. Slicing it in smaller
piece should clarify it.

(This is a gratuitous cleanup that I made while investigating a bug).

extern crate cc;

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