> I cannot find libspatialindex 1.9.3 here:
>
> https://download.osgeo.org/libspatialindex/

I have fixed this now.

> How could you build it (Probably answer: You guix downloaded it in
> your store and it was found by the right checksum)?

That's probably what happened, I guess.

> I found a download link here:
>
> https://libspatialindex.org/#download
>
> Or we better take the git sources? Could you please update the patch?

Let's use the source tarball for now. I think it's stable enough and the
link won't break again.

Yes, we should use proj instead of proj.4 wherever possible. But, if I
remember correctly, some packages work only with proj.4 for now. Also,
we should push some of the simpler patches (say, the simple update
patches) to master right away. That will help to declutter this bug
report a little bit. WDYT?

Please find attached a new patchset. Around 56 tests are still failing
in the qgis build. I brought it down from around a 100 or so.