libngspice: fix build on Darwin with Clang

Apply patch to remove redundant is_compound specialization in cppduals.
This resolves a compilation error on macOS where the specialization
conflicts with the standard library's type traits.

pkgs/by-name/li/libngspice/package.nix

@@ -21,6 +21,24 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-8arYq6woKKe3HaZkEd6OQGUk518wZuRnVUOcSQRC1zQ=";
   };
 
+  patches = [
+    (builtins.toFile "fix-cppduals.patch" ''
+      --- a/src/include/cppduals/duals/dual
+      +++ b/src/include/cppduals/duals/dual
+      @@ -485,10 +485,6 @@ struct is_arithmetic<duals::dual<T>> : is_arithmetic<T> {};
+
+       #endif // CPPDUALS_ENABLE_IS_ARITHMETIC
+
+      -/// Duals are compound types.
+      -template <class T>
+      -struct is_compound<duals::dual<T>> : true_type {};
+      -
+       // Modification of std::numeric_limits<> per
+       // C++03 17.4.3.1/1, and C++11 18.3.2.3/1.
+       template <class T>
+    '')
+  ];
+
   nativeBuildInputs = [
     flex
     bison