bug#40420: 28.0.50; [feature/native-comp] referencing the build directory

[Formbi]

Gccemacs references the build directory in the final thing. This is a problem 
especially in Guix, because Guix removes the build directory after building a 
package and you get something like this:
emacs: 
/tmp/guix-build-gccemacs-28.0.50-0.00ee320.drv-0/gccemacs-28.0.50-0.00ee320-checkout/lisp/eln-x86_64-pc-linux-gnu-3542fae6089df671/custom.eln:
 cannot open shared object file: No such file or directory