encfs: fix build with newer versions of clang

Apply patch to resolve the following error:

    error: no matching constructor for initialization of 'std::shared_ptr<AbstractCipherKey>'

pkgs/tools/filesystems/encfs/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub
+{ lib, stdenv, fetchFromGitHub, fetchpatch
 , cmake, pkg-config, perl
 , gettext, fuse, openssl, tinyxml2
 }:
@@ -14,6 +14,15 @@ stdenv.mkDerivation rec {
     owner = "vgough";
   };
 
+  patches = lib.optionals stdenv.cc.isClang [
+    # Fixes a build failure when building with newer versions of clang.
+    # https://github.com/vgough/encfs/pull/650
+    (fetchpatch {
+      url = "https://github.com/vgough/encfs/commit/406b63bfe234864710d1d23329bf41d48001fbfa.patch";
+      hash = "sha256-VunC5ICRJBgCXqkr7ad7DPzweRJr1bdOpo1LKNCs4zY=";
+    })
+  ];
+
   buildInputs = [ gettext fuse openssl tinyxml2 ];
   nativeBuildInputs = [ cmake pkg-config perl ];