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

[Eli Zaretskii]

> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
> Date: Wed, 04 Dec 2019 20:02:12 +0100
> 
> For some reason, one of my setups[1] experiences a pure storage overflow
> with the current master[2].  Searching previous bug reports for the
> warning[3] led me to understand that increasing BASE_PURESIZE in
> src/puresize.h would solve the issue; since I didn't have the patience
> to recompile possibly multiple times, I tried to find a way to know
> exactly how much I should increase this value.
> 
> I noticed that Fdump_emacs uses check_pure_size from alloc.c to print a
> warning before dumping when this happens.  The following patch exposes
> check_pure_size when we HAVE_PDUMPER, so that Fdump_emacs_portable can
> use it too.

I'm not sure we should care about overflowing the pure space in
pdumped Emacs.  Why does it matter?  It mattered in unexec'ed Emacs,
that's why we warned about it.  Maybe the right solution is to remove
the warning from startup.el instead.

Daniel, what are your thoughts about this?