libgdal-core is getting rebuilt for each plugin

[akrherz]

          > For some reason, core files are rebuilt.

This seems to be a different problem that really causes our build time to explode.

Originally posted by @akrherz in #1023 (comment)

[rouault]

This seems to be a different problem that really causes our build time to explode.

looking more closely at the logs, it is not that dramatic. At least it is far from being a rebuild of the whole libgdal-core. A subset of files that in theory shouldn't be rebuilt are rebuilt, presumably because there's a difference in dependencies installed between the libgdal-core build and the plugins.
For the subset of drivers for which it has been implemented, which would probably be only Arrow/Parquet for the sake of conda-forge builds, we could use the 3.10 new "standalone" build mode, like demonstrated in https://github.com/OSGeo/gdal/blob/aae18ed5e393949498072ad1269856d445869314/.github/workflows/ubuntu_20.04/build.sh#L60-L74 , that really only builds the driver that is explicitly asked to be built. This assumes libgdal-core is installed somewhere. Not sure how well this plays with conda-forge builds.