bug#59658: native-compile-prune-cache deletes *.eln files in the build's native-lisp directories

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Mon, 28 Nov 2022 15:11:10 +0100
> 
> This is on Windows, and running Emacs in-place after building from trunk (no 
> installation).
> 
> If you have several VERSION-xxxxxxxx directories under native-lisp/ and do 
> 
> M-x native-compile-prune-cache <RET>
> 
> this deletes any .eln files in the VERSION-xxxxxxxx directories of the stale 
> caches. Their preloaded/
> subdirectories and content are not affected.
> 
> Presumably this should skip the last entry in native-comp-eln-load-path, 
> which is documented as being
> "assumed to be the system one".

Yes, I think it should skip the last entry.  AFAIR, that was the intent with
this command, in which case what it does now is an oversight of sorts.