Merge pull request #9794 from taku0/libao_for_darwin

libao: enable libcap only on Linux

pkgs/development/libraries/libao/default.nix

···
   };
 
   buildInputs =
-    [ pkgconfig libcap ] ++
-    lib.optional stdenv.isLinux (if usePulseAudio then libpulseaudio else alsaLib);
+    [ pkgconfig ] ++
+    lib.optional stdenv.isLinux (if usePulseAudio then libpulseaudio else alsaLib) ++
+    lib.optional stdenv.isLinux libcap;
 
   meta = {
     longDescription = ''