libcdio: broaden platforms

From the homepage:

> The cdparanoia library and cdparanoia command are included making
> this the only single-source cdparanoia that works on FreeBSD,
> NetBSD, OSX, cygwin, Solaris, BSDI as well as GNU/Linux.

Builds fine for FreeBSD and NetBSD.

pkgs/development/libraries/libcdio/default.nix

@@ -46,6 +46,6 @@ stdenv.mkDerivation rec {
     '';
     homepage = "https://www.gnu.org/software/libcdio/";
     license = licenses.gpl2Plus;
-    platforms = platforms.linux ++ platforms.darwin;
+    platforms = platforms.unix;
   };
 }