Fatal error on misuse of binding operators

[stedolan]

A fatal_error in Typecore.type_binding_op_ident is reachable if a binding operator is defined inside a class:

class c =
  let (let*) x f = f x in
  object
    method foo = let* x = 1 in x
  end

>> Fatal error: Illegal name for instance variable
Fatal error: exception Misc.Fatal_error

(I don't see anything wrong with issuing an error here, it's weird code. But it should be an actual error with a location, not a crash)

[github-actions]

This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc.