ocamlnet: fixup build by bringing back nettle-3.3

pkgs/development/libraries/nettle/3.3.nix

@@ -0,0 +1,10 @@
+{ callPackage, fetchurl, ... } @ args:
+
+callPackage ./generic.nix (args // rec {
+  version = "3.3";
+
+  src = fetchurl {
+    url = "mirror://gnu/nettle/nettle-${version}.tar.gz";
+    sha256 = "07mif3af077763vc35s1x8vzhzlgqcgxh67c1xr13jnhslkjd526";
+  };
+})

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

@@ -1,5 +1,11 @@
 { stdenv, fetchurl, pkgconfig, ncurses, ocaml, findlib, ocaml_pcre, camlzip
-, gnutls, nettle }:
+, gnutls, nettle_3_3 }:
+
+# These overrides are just temporary, until ocamlnet supports nettle-3.4.
+let gnutls_orig = gnutls; in
+let gnutls = gnutls_orig.override { nettle = nettle_3_3; };
+    nettle = nettle_3_3;
+in
 
 let version = "4.1.4"; in