audiofile: Use alsaLib for native Linux only.

Using ALSA for non-Linux systems really doesn't make much sense, so
using buildNativeInputs to ensure it won't be used for cross-builds.

Of course, if you're cross-building to Linux, the dependency won't be
used, but right now we don't have a good way to easily check whether the
cross target is Linux.

Signed-off-by: aszlig <[e-mail]>

pkgs/development/libraries/audiofile/default.nix

···
 stdenv.mkDerivation rec {
   name = "audiofile-0.3.6";
 
-  buildInputs = stdenv.lib.optional (!stdenv.isDarwin) alsaLib;
+  nativeBuildInputs = stdenv.lib.optional stdenv.isLinux alsaLib;
 
   src = fetchurl {
     url = "http://audiofile.68k.org/${name}.tar.gz";