concatenate to a temporary file for more robustness.

    (lisp-compilation-output-files o s))

  (defmethod perform ((o basic-concatenate-source-op) (s system))

    (let ((inputs (input-files o s))

          (output (output-file o s)))

      (concatenate-files inputs output)))

    (let* ((ins (input-files o s))

           (out (output-file o s))

           (tmp (tmpize-pathname out)))

      (concatenate-files ins tmp)

      (rename-file-overwriting-target tmp out)))

  (defmethod perform ((o basic-load-concatenated-source-op) (s system))

    (perform-lisp-load-source o s))

  (defmethod perform ((o basic-compile-concatenated-source-op) (s system))