gnu: jack: Don't install to "lib64" on 64-bit platforms.

* gnu/packages/audio.scm (jack-1)[arguments]: New field.

gnu/packages/audio.scm

@@ -1393,6 +1393,14 @@ especially for creating reverb effects.  It supports impulse responses with 1,
               (base32
                "0i6l25dmfk2ji2lrakqq9icnwjxklgcjzzk65dmsff91z2zva5rm"))))
     (build-system gnu-build-system)
+    (arguments
+     `(#:phases (modify-phases %standard-phases
+                  (add-after 'unpack 'patch-configure
+                    (lambda _
+                      (substitute* "configure"
+                        ;; Install to <out/lib> regardless of platform.
+                        (("libnn=lib64") "libnn=lib"))
+                      #t)))))
     (inputs
      `(("alsa-lib" ,alsa-lib)
        ("readline" ,readline)))