gnu: ld-wrapper: Use _IOLBF on Guile 2.0 only.

* gnu/packages/base.scm (make-ld-wrapper)[arguments]: Wrap use of
'_IOLBF' in 'cond-expand' and use 'line instead on Guile > 2.0.

gnu/packages/base.scm

@@ -546,7 +546,9 @@ (define* (make-ld-wrapper name #:key
                                       '(string-append bin "/ld")))
                             (go  (string-append ld ".go")))
 
-                       (setvbuf (current-output-port) _IOLBF)
+                       (setvbuf (current-output-port)
+                                (cond-expand (guile-2.0 _IOLBF)
+                                             (else 'line)))
                        (format #t "building ~s/bin/ld wrapper in ~s~%"
                                (assoc-ref %build-inputs "binutils")
                                out)