libcdio: depend on libiconv unconditionally

libiconv is already defined per-platform.  The actual libiconv library
won't be built on platforms like Linux where it doesn't need to be, so
there's no need to maintain a separate platform list here.

Required to build for FreeBSD.

pkgs/development/libraries/libcdio/default.nix

@@ -31,8 +31,8 @@ stdenv.mkDerivation rec {
   '';
 
   nativeBuildInputs = [ pkg-config help2man ];
-  buildInputs = [ libcddb ncurses ]
-    ++ lib.optionals stdenv.isDarwin [ libiconv Carbon IOKit ];
+  buildInputs = [ libcddb libiconv ncurses ]
+    ++ lib.optionals stdenv.isDarwin [ Carbon IOKit ];
 
   doCheck = !stdenv.isDarwin;