libjack2: fix cross

Always defaults to unprefixed pkg-config, even when cross-compiling.

Fixes: https://github.com/NixOS/nixpkgs/issues/96548

pkgs/misc/jackaudio/default.nix

@@ -48,6 +48,9 @@ stdenv.mkDerivation rec {
         --replace /bin/bash ${bash}/bin/bash
   '';
 
+  PKGCONFIG = "${stdenv.cc.targetPrefix}pkg-config";
+
+  dontAddWafCrossFlags = "true";
   wafConfigureFlags = [
     "--classic"
     "--autostart=${if (optDbus != null) then "dbus" else "classic"}"