libvisual: disable building examples when cross compiling

the examples depend on SDL, and sdl-config is not available when crossing

pkgs/development/libraries/libvisual/default.nix

@@ -4,6 +4,8 @@
 , SDL
 , glib
 , pkg-config
+  # sdl-config is not available when crossing
+, withExamples ? stdenv.buildPlatform == stdenv.hostPlatform
 }:
 
 stdenv.mkDerivation rec {
@@ -16,7 +18,9 @@ stdenv.mkDerivation rec {
   };
 
   nativeBuildInputs = [ pkg-config ];
-  buildInputs = [ SDL glib ];
+  buildInputs = lib.optional withExamples SDL ++ [ glib ];
+
+  configureFlags = lib.optional (!withExamples) "--disable-examples";
 
   meta = {
     description = "An abstraction library for audio visualisations";