message: Fix building with -j1 flag
diff: @@ -222,7 +222,24 @@ fn build_compiler(opencv: &Library) -> cc::Build {
  }
  fn build_job_server() -> Option<jobserver::Client> {
  - unsafe { jobserver::Client::from_env() }.or_else(|| {
  + unsafe { jobserver::Client::from_env() }
  + .and_then(|c| {
  + let available_jobs = c.available().unwrap_or(0);
  + if available_jobs > 0 {
  + eprintln!(
  + "=== Using environment job server with the the amount of available jobs: {}",
  + available_jobs
  + );
  + Some(c)
  + } else {
  + eprintln!(
  + "=== Available jobs from the environment created jobserver is: {} or there is an error reading that value",
  + available_jobs
  + );
  + None
  + }
  + })
  + .or_else(|| {
  let num_jobs = env::var("NUM_JOBS")
  .ok()
  .and_then(|jobs| jobs.parse().ok())
  