bug#20614: Segmentation fault when building on Power8 Little Endian

[Eli Zaretskii]

> Cc: 20614@debbugs.gnu.org
> From: Petr Hracek <phracek@redhat.com>
> Date: Mon, 5 Oct 2015 13:23:42 +0200
> 
> But if fails with
> /home/phracek/rpmbuild/BUILD/emacs-24.3/src/unexelf.c:1263: undefined 
> reference to `valid_pointer_p'

That function is static, so it's only known in alloc.c.  Either remove
the 'static' qualifier from it, or copy it to unexelf.c.