Hello,

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.