bug#43137: 28.0.50; [feature/native-comp] .eln path fixup confused using relative paths

[Andreas Fuchs]

For the exec-path issue, I have a patch here: https://github.com/emacs-mirror/emacs/commit/2c91d2c0fef162ecce87915863931bea47305eac; this ensures running `emacs` from PATH on my system finds the right binary, and lets emacs start up (there is a weird delay though, which may well be my system being creaky).

The same branch that this change is on, I also have a change to build a separate .pdmp file for the macOS app bundle - but that set of changes isn't yet correct. It still picks up the wrong file name, still.

However, good news: One part of the bug is dead, at least (: