fn php_config(arg: &str) -> Result<String> {
        let cmd = Command::new(Self::find_bin()?)
            .arg(arg)
            .output()
            .context("Failed to run `php-config`")?;
        let stdout = String::from_utf8_lossy(&cmd.stdout);
        if !cmd.status.success() {
            let stderr = String::from_utf8_lossy(&cmd.stderr);
            bail!("Failed to run `php-config`: {} {}", stdout, stderr);
        }
        Ok(stdout.to_string())
    }
Runs `php-config` with one argument, returning the stdout.
unix_build.rs