Turn more licenses into lib.licenses style

Should eval cleanly, as far as -A tarball tells me.

Relevant: issue #2999, issue #739

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

@@ -27,7 +27,7 @@ stdenv.mkDerivation {
   meta = {
     homepage = http://dypgen.free.fr;
     description = "Dypgen GLR self extensible parser generator";
-    license = "CeCILL-B_V1";
+    license = stdenv.lib.licenses.cecill-b;
 #    maintainers = [ stdenv.lib.maintainers.roconnor ];
   };
 }

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

@@ -37,7 +37,7 @@ stdenv.mkDerivation {
   meta = {
     homepage = http://ocamlgraph.lri.fr/;
     description = "Graph library for Objective Caml";
-    license = "GNU Library General Public License version 2, with the special exception on linking described in file LICENSE";
+    license = stdenv.lib.licenses.gpl2Oss;
     platforms = ocaml.meta.platforms;
     maintainers = [
       stdenv.lib.maintainers.kkallio

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

@@ -21,7 +21,7 @@ stdenv.mkDerivation {
   meta = {
     description = "OCaml native toplevel";
     homepage = http://benediktmeurer.de/ocamlnat/;
-    license = "QPL";
+    license = stdenv.lib.licenses.qpl;
     longDescription = ''
       The ocamlnat project provides a new native code OCaml toplevel
       ocamlnat, which is mostly compatible to the byte code toplevel ocaml,

pkgs/development/ocaml-modules/ocsigen-deriving/default.nix

@@ -7,7 +7,7 @@ stdenv.mkDerivation {
     rev = "refs/tags/0.6.2";
     sha256 = "2b3bf3f4972d0e6eaf075f7353ce482b776726e0cd04947a89b7156384ec0662";
     };
-  
+
   buildInputs = [ocaml findlib ocaml_oasis ocaml_data_notation ocaml_optcomp];
 
   configurePhase = ''
@@ -21,7 +21,7 @@ stdenv.mkDerivation {
   meta =  {
     homepage = https://github.com/ocsigen/deriving;
     description = "Extension to OCaml for deriving functions from type declarations";
-    license = "MIT";
+    license = stdenv.lib.licenses.mit;
     platforms = ocaml.meta.platforms;
     maintainers = [
       stdenv.lib.maintainers.gal_bolle