bug#58513: describe-function should say that defconst variables are constant

[Stefan Kangas]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> And we could start adding a symbol property saying that a constant is
> meant to be constant, and perhaps start warning if people change it, but
> that would make things slower for basic things like `setq', so I'm
> pretty sure it's not worth it.

Yes, incurring a run-time cost doesn't sound worth it, but we could
perhaps make the byte-compiler warn about it.