lv2: support cross-compilation

The waf cross flags seem to not be useful for most packages, to me.
I'll just set the flag for now, but maybe turning it around
may be more useful to do somewhere in the future.

pkgs/development/libraries/audio/lv2/default.nix

@@ -22,6 +22,7 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [
     pkg-config
     wafHook
+    python3
   ];
 
   buildInputs = [
@@ -35,6 +36,7 @@ stdenv.mkDerivation rec {
   ] ++ lib.optionals stdenv.isDarwin [
     "--lv2dir=${placeholder "out"}/lib/lv2"
   ];
+  dontAddWafCrossFlags = true;
 
   passthru.tests = {
     inherit pipewire;