bug#66912: With `require', the byte compiler reports the wrong file for errors.

[Stefan Monnier]

> Here's the amended patch.  It's a lot shorter (and easier) than the
> previous version.  I would like to commit it as the fix to bug#66912.

Thanks.  I'm not in love with this approach, among other things because
of the problem I described earlier:

    But I don't think it would be correct in all cases: if file A loads
    file B which compiles file C which loads file D which signals an
    error we want the compiler error message to say "error in D loaded
    from C" and not "error in D loaded from C loaded from B loaded from
    A".

but it's not the end of the world, so I don't object to installing it on
`master`.

>  static Lisp_Object Vloads_in_progress;
> +/* The same as the above, except it survives the unbinding done in the
> +   event of an error, and can thus be used in error handling.  */
> +Lisp_Object Vloads_still_in_progress;

Please clarify how "it survives the unbinding".

[ BTW, a nice improvement would be to keep track of where we are in the
  outer load when the start the inner load, so that the "While loading"
  message can point to the place where the loading was triggered.  ]


        Stefan