treewide: use ocaml.version (#19192)

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

@@ -1,14 +1,12 @@
 {stdenv, fetchurl, ocaml, findlib, gdome2, libxslt, pkgconfig}:
 
 let
-  ocaml_version = (builtins.parseDrvName ocaml.name).version;
-  version = "0.2.6";
   pname = "gmetadom";
-
 in
 
-stdenv.mkDerivation {
+stdenv.mkDerivation rec {
   name = "${pname}-${version}";
+  version = "0.2.6";
 
   src = fetchurl {
     url = "mirror://sourceforge/project/${pname}/${pname}/${version}/${pname}-${version}.tar.gz";
@@ -20,7 +18,7 @@ stdenv.mkDerivation {
   dontDisableStatic = true;
 
   preConfigure=''
-    configureFlags="--with-ocaml-lib-prefix=$out/lib/ocaml/${ocaml_version}/site-lib"
+    configureFlags="--with-ocaml-lib-prefix=$out/lib/ocaml/${ocaml.version}/site-lib"
   '';