Correct a condition to request jobserver tokens

This looks like it was a bug ever present from the original
implementation of a GNU jobserver in rust-lang#4110, but we currently
unconditionally request a token is allocated for any job we pull off our
job queue. Rather we only need to request tokens for everything but the
first job because we already have an implicit token for that job.

src/cargo/core/compiler/job_queue.rs

@@ -230,7 +230,7 @@ impl<'a, 'cfg> JobQueue<'a, 'cfg> {
             // request a token.
             while let Some((key, job)) = self.queue.dequeue() {
                 queue.push((key, job));
-                if !self.active.is_empty() || !queue.is_empty() {
+                if self.active.len() + queue.len() > 1 {
                     jobserver_helper.request_token();
                 }
             }