To be able to load Cabs_debug in ocamldebug, we need to avoid depending on
external c functions.

       because always true now

initial version of the patch contributed by madroach at
https://bts.frama-c.com/view.php?id=2458

(blind make headers from specifications)

- Fix Value/Value#5
- Fix Value/Value#14

Some case studies (e.g. dyad) use some ugly casts from fd_set_t which lead
to the analysis stopping too early.
Changing the representation of fd_set_t should also help it better conform to
the standard (since a fd_set_t should be able to hold FD_SETSIZE elements).

[Ptests] preserve LOG after STDOPT directive

See merge request frama-c/frama-c!2073

This is absolutely not a sneaky attempt to relaunch a build (now that OCI seems
in better shape) pushing a nearly empty commit.