The main purpose of these jobs is to only package the strict necessary
for a working GIMP under Windows, i.e. getting rid of all unnecessary
executables, and inspecting binary dependencies recursively to only
package used DLLs.

The dll_link.py script is taken from Siril codebase (see commit a86e82a8
on Siril repository, by FlorianBen). This was a very nice idea, and
makes for much smaller test archive (Siril is also GPLv3 so licensing is
ok for the reuse, also anyway it's just a small independent build
script).
Moreover having it as a separate job allows to have artifacts with only
the finale distribution (artifacts on the build job also have the build
directory and the whole prefix, which we want to keep in order to debug
when needed).

Hopefully I am not missing anything. Siril seems to package more, like
various gdk-pixbuf-*.exe, gspawn-*.exe and gdbus.exe. I am wondering if
these are actually necessary. I could run GIMP fine without these in
quick tests, but I guess I'll have to investigate a bit more to figure
this out. That's what nightly builds are for, after all, so hopefully
people will report if we miss some runtime dependencies.