bug#38492: 27.0.50; Warn pdumper users when pure space has been overflowed

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> > We should probably consider just removing the pure space mechanism at 
>> > some point. 
>> Does this mean you agree with removing the warning in startup.el 
>> about overflowed pure space?
> Yes. 

Why?

This warning was placed because we needed to disable GC in dumps that
had overflown the purespace, so the dumped Emacs was not
fully functional.

I see that with the current pdump we don't disable GC in dumps that
overflew the purespace.  Why is that?

IIRC, the problem with running GC in an Emacs with overflown purespace
is that overflowing the purespace created pointers from the purespace to
the heap and those aren't traced by the GC so it resulted in core dumps.

I can't exactly remember the cases where this happened, but I can't see
why the pdumper would be less affected than the unexec code.

I see that the code has a slightly different explanation:

    /* Can't GC if pure storage overflowed because we can't determine
       if something is a pure object or not.  */
    garbage_collection_inhibited++;

but that comment similarly seems to apply to pdump just as much as it
applies to unexec.


        Stefan