Don't run ocaml through ocamlrun on non-Windows

seems it doesn't always work depending on the installed ocaml; and the
workaround is only needed on Windows (for the record: the reason for
that had to do with losing the process handle on Windows when ocamlrun
got called automatically due to #!)

src/cfg.ml

@@ -68,6 +68,7 @@ let char_width = ref 8 (* Computed once the text view is initialized *)
 
 let theme = ref "dark"
 
-let ocaml_cmd = ref "ocamlrun"
-
-let ocaml_opts : string list ref = ref ["ocaml"]
+let ocaml_cmd, ocaml_opts =
+  if Sys.os_type = "Win32"
+  then ref "ocamlrun", ref ["ocaml"]
+  else ref "ocaml", ref []