buildDunePackage: new support function; use it to refactor some OCaml derivations

pkgs/development/ocaml-modules/ezjsonm/default.nix

@@ -1,27 +1,20 @@
-{ stdenv, fetchzip, ocaml, findlib, dune, jsonm, hex, sexplib }:
+{ stdenv, fetchzip, buildDunePackage, jsonm, hex, sexplib }:
 
-let version = "0.6.0"; in
-
-stdenv.mkDerivation {
-  name = "ocaml${ocaml.version}-ezjsonm-${version}";
+buildDunePackage rec {
+  pname = "ezjsonm";
+  version = "0.6.0";
 
   src = fetchzip {
-    url = "https://github.com/mirage/ezjsonm/archive/${version}.tar.gz";
+    url = "https://github.com/mirage/${pname}/archive/${version}.tar.gz";
     sha256 = "18g64lhai0bz65b9fil12vlgfpwa9b5apj7x6d7n4zzm18qfazvj";
   };
 
-  buildInputs = [ ocaml findlib dune ];
   propagatedBuildInputs = [ jsonm hex sexplib ];
 
-  buildPhase = "dune build -p ezjsonm";
-
-  inherit (dune) installPhase;
-
   meta = {
     description = "An easy interface on top of the Jsonm library";
     homepage = https://github.com/mirage/ezjsonm;
     license = stdenv.lib.licenses.isc;
     maintainers = with stdenv.lib.maintainers; [ vbgl ];
-    platforms = ocaml.meta.platforms or [];
   };
 }