message: Fix jobserver_exists test on single-cpu systems
  Closes
diff: @@ -51,7 +51,10 @@ fn jobserver_exists() {
  .file("src/lib.rs", "")
  .build();
  - p.cargo("build").run();
  + // Explicitly use `-j2` to ensure that there's eventually going to be a
  + // token to read from `valdiate` above, since running the build script
  + // itself consumes a token.
  + p.cargo("build -j2").run();
  }
  #[cargo_test]
  