gnu: lablgtk: use ocamlfind in installation

* gnu/packages/ocaml.scm (lablgtk): Use ocamlfind in installation.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/ocaml.scm

@@ -507,6 +507,7 @@ Knuth’s LR(1) parser construction technique.")
     (native-inputs
      `(("camlp4" ,camlp4)
        ("ocaml" ,ocaml)
+       ("findlib" ,ocaml-findlib)
        ("pkg-config" ,pkg-config)))
     ;; FIXME: Add inputs gtkgl-2.0, libpanelapplet-2.0, gtkspell-2.0,
     ;; and gtk+-quartz-2.0 once available.
@@ -521,21 +522,24 @@ Knuth’s LR(1) parser construction technique.")
      `(#:tests? #f ; no check target
 
        ;; opt: also install cmxa files
-       #:make-flags (list "all" "opt")
+       #:make-flags (list "all" "opt"
+                          (string-append "FINDLIBDIR="
+                                         (assoc-ref %outputs "out")
+                                         "/lib/ocaml"))
        ;; Occasionally we would get "Error: Unbound module GtkThread" when
        ;; compiling 'gtkThInit.ml', with 'make -j'.  So build sequentially.
        #:parallel-build? #f
 
        #:phases
          (modify-phases %standard-phases
-           (replace 'install
+           (add-before 'install 'prepare-install
              (lambda* (#:key inputs outputs #:allow-other-keys)
                (let ((out (assoc-ref outputs "out"))
                      (ocaml (assoc-ref inputs "ocaml")))
                  ;; Install into the output and not the ocaml directory.
+                 (mkdir-p (string-append out "/lib/ocaml"))
                  (substitute* "config.make"
                    ((ocaml) out))
-                 (system* "make" "old-install")
                  #t))))))
     (home-page "http://lablgtk.forge.ocamlcore.org/")
     (synopsis "GTK+ bindings for OCaml")