cln: fix build on darwin

See https://github.com/NixOS/nixpkgs/pull/162265#issuecomment-1100467765

pkgs/development/libraries/cln/default.nix

@@ -1,10 +1,14 @@
-{ lib, stdenv, fetchurl, gmp }:
+{ lib, stdenv, fetchurl, fetchgit, gmp }:
 
 stdenv.mkDerivation rec {
   pname = "cln";
   version = "1.3.6";
 
-  src = fetchurl {
+  src = if stdenv.isDarwin then fetchgit {
+    url = "git://www.ginac.de/cln.git";
+    rev = "cln_${builtins.replaceStrings [ "." ] [ "-" ] version}";
+    sha256 = "sha256-P32F4TIDhE2Dwzydq8iFK6ch3kICJcXeeXHs5PBQG88=";
+  } else fetchurl {
     url = "${meta.homepage}${pname}-${version}.tar.bz2";
     sha256 = "0jlq9l4hphk7qqlgqj9ihjp4m3rwjbhk6q4v00lsbgbri07574pl";
   };