!1940 added support for soup 3, including a fallback to soup 2.4
where the newer version isn't available.
Unfortunately it missed that libgweather has a hidden soup dependency,
and now gnome-shell fails to start if a weather location has been set
up and soup 3 is available.
We don't have a good way to detect that case, so hide the soup 3 support
behind a build option. Distributors are expected to switch it at the
same time as libgweather.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1966>