write-c2ffi: WITH-OUTPUT-TO-TEMPORARY-FILE from CL-FAD 0.7.2 returns a pathname

From CL-FAD 0.7.2, file `quicklisp/dists/quicklisp/software/cl-fad-0.7.2/temporary-files.lisp`:
```
(defmacro with-output-to-temporary-file ((stream &rest args) &body body)
  "Create a temporary file using OPEN-TEMPORARY with ARGS and run BODY
  with STREAM bound to the temporary file stream.  Returns the
  pathname of the file that has been created.  See OPEN-TEMPORARY for
  permitted options."
  `(with-open-stream (,stream (open-temporary ,@args))
     ,@body
     (pathname ,stream)))
```