ocaml: fix cross-compile by adding bootstrapping ocaml

Fixes cross compilation looking for ocamlc:

checking if the installed OCaml compiler can build the cross compiler... ./configure: line 4348: ocamlc: command not found
no (5.4.1 vs )
configure: error: exiting

Assisted-by: DeepSeek V4 Flash

pkgs/development/compilers/ocaml/generic.nix

@@ -21,6 +21,7 @@ in
   ncurses,
   binutils,
   buildEnv,
+  pkgsBuildBuild,
   libunwind,
   fetchpatch,
   libx11,
@@ -177,6 +178,7 @@ stdenv.mkDerivation (
         ]
       else
         [ "nixpkgs_world" ];
+    nativeBuildInputs = optional (stdenv.hostPlatform != stdenv.targetPlatform) pkgsBuildBuild.ocaml;
     buildInputs =
       optional (lib.versionOlder version "4.07") ncurses
       ++ optionals useX11 [