ocamlPackages.ptime: allow switching off js_of_ocaml support

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

···
-{ stdenv, lib, fetchurl, ocaml, findlib, ocamlbuild, topkg, result, js_of_ocaml }:
+{ stdenv, lib, fetchurl, ocaml, findlib, ocamlbuild, topkg, result, js_of_ocaml
+, jsooSupport ? true
+}:
 
 stdenv.mkDerivation rec {
   version = "0.8.5";
···
   };
 
   nativeBuildInputs = [ ocaml findlib ocamlbuild ];
-  buildInputs = [ findlib topkg js_of_ocaml ];
+  buildInputs = [ findlib topkg ]
+    ++ lib.optional jsooSupport js_of_ocaml;
 
   propagatedBuildInputs = [ result ];
 
-  buildPhase = "${topkg.run} build --with-js_of_ocaml true";
+  buildPhase = "${topkg.run} build --with-js_of_ocaml ${lib.boolToString jsooSupport}";
 
   inherit (topkg) installPhase;