AFAIU the issue which it tried to fix only happens on custom builds and it looks
to me that it's just about multi-prefixes developer builds which were not
configured with -Drelocatable-bundle=no as they should.
When you compile GIMP yourself and intend to run it in a multi-prefix
environment, without ever relocating the build, like on Unix-like systems, then
disable this feature.
In any case, we should never do this kind of system file moving hacks in our
build system. The MSYS2 project even had to patch this out:
https://gitlab.gnome.org/GNOME/gimp/-/merge_requests/1171#note_2022406
a3c0b515f9