bug#52488: Try basename of agrv0's realpath for .pdmp lookup in libexecdir

[Glenn Morris]

Ken Brown wrote:

> I think the problem is that load_pdmp doesn't look in libexecdir for a
> .pdmp file whose name matches the name of the emacs executable. For
> example, suppose I have a symlink /usr/bin/emacs that resolves to
> /usr/bin/emacs-nox.exe. Then load_pdmp looks for
> /usr/bin/emacs-nox.pdmp, but it doesn't look for
> /usr/libexec/emacs/28.0.90/x86_64-pc-cygwin/emacs-nox.pdmp.

Note that in Emacs 29 it uses the fingerprint in the pdmp name,
so that issue should not occur.

(cf https://debbugs.gnu.org/43050)