Fix dist build

[sim642]

Currently dune build gobview in Goblint's repository only builds Gobview half-way: it does the js_of_ocaml compilation, but doesn't actually create the dist directory that Goblint tries to use with --enable gobview.

TODO

• This doesn't still work because it requires Directory targets that contain symlinks ocaml/dune#5945, which is to be released in dune 3.5.0.