adds minimal error-handling

Now instead of ignoring errors and spoiling stderr, we capture the
output and failwith the captured message.

otherlibs/site/src/plugins/linker/toplevel/linker.ml

@@ -1 +1,10 @@
-let load = Topdirs.dir_load Format.err_formatter
+let load filename =
+  let buf = Buffer.create 16 in
+  let ppf = Format.formatter_of_buffer buf in
+  match Toploop.load_file ppf filename with
+  | true -> ()
+  | false ->
+    Format.pp_print_flush ppf ();
+    failwith
+    @@ Format.asprintf "Failed to load file `%s': %s" filename
+         (Buffer.contents buf)