Merge pull request ocaml#3855 from dra27/builtin-graphics

Detect graphics library for OCaml < 4.09

src/dune_rules/findlib/meta.ml

@@ -224,6 +224,7 @@ let builtins ~stdlib_dir ~version:ocaml_version =
         ]
     }
   in
+  let graphics = simple "graphics" [] ~dir:"+" in
   let libs =
     let base =
       [ stdlib; compiler_libs; str; unix; bigarray; threads; dynlink; bytes ]
@@ -246,6 +247,12 @@ let builtins ~stdlib_dir ~version:ocaml_version =
       else
         base
     in
+    let base =
+      if Path.exists (Path.relative stdlib_dir "graphics.cma") then
+        graphics :: base
+      else
+        base
+    in
     (* We do not rely on an "exists_if" ocamlfind variable, because it would
        produce an error message mentioning a "hidden" package (which could be
        confusing). *)