bug#33014: 26.1.50; 27.0.50; Fatal error after re-evaluating a thread's function

[Gemini Lasswell]

Eli Zaretskii <eliz@gnu.org> writes:

>> I have patched Emacs with a 'volatile' on the definition of 'fun' in
>> Ffuncall, and so far haven't managed to reproduce the bug with it:
>
> Thanks.  This needs a comment for why we do something strange like
> that, but otherwise, if no one has better ideas in a week's time,
> let's install this.

Pushed to master, along with a new test which should fail if some future
optimizing compiler removes the reference from the stack in spite of the
'volatile'.