Add patches/ocaml-system/gen_ocaml_config.ml.in.after-5.4.0

patches/ocaml-system/gen_ocaml_config.ml.in.after-5.4.0

@@ -0,0 +1,34 @@
+let () =
+  let exe = ".exe" in
+  let ocamlc =
+    let (base, suffix) =
+      let s = Sys.executable_name in
+      if Filename.check_suffix s exe then
+        (Filename.chop_suffix s exe, exe)
+      else
+        (s, "") in
+    base ^ "c" ^ suffix in
+  let ocamlc_digest = Digest.to_hex (Digest.file ocamlc) in
+  let libdir =
+    if Sys.command (ocamlc^" -where > %{_:name}%.config") = 0 then
+      let ic = open_in "%{_:name}%.config" in
+      let r = input_line ic in
+      close_in ic;
+      Sys.remove "%{_:name}%.config";
+      r
+    else
+      failwith "Bad return from 'ocamlc -where'"
+  in
+  let graphics = Filename.concat libdir "graphics.cmi" in
+  let graphics_digest =
+    if Sys.file_exists graphics then
+      Digest.to_hex (Digest.file graphics)
+    else
+      String.make 32 '0'
+  in
+  let oc = open_out "%{_:name}%.config" in
+  Printf.fprintf oc "opam-version: \"2.0\"\n\
+                     file-depends: [ [ %%S %%S ] [ %%S %%S ] ]\n\
+                     variables { path: %%S }\n"
+    ocamlc ocamlc_digest graphics graphics_digest (Filename.dirname ocamlc);
+  close_out oc