To get PostGIS going on Darwin:
1. Add libiconv, as is often required.
2. Expand platforms to `platforms.all`.
3. Deal with PostGIS' quirky build system.
PostGIS' configure.ac has the following gem:
AC_MSG_RESULT([------------------------------------------------------------------------])
AC_MSG_RESULT([ WARNING: You have set the --prefix to '$prefix'. But we mostly ])
AC_MSG_RESULT([ ignore the --prefix. For your info, using the values determined from ])
AC_MSG_RESULT([ $PG_CONFIG we will be installing: ])
AC_MSG_RESULT([ * postgis shared library in $PGSQL_LIBDIR ])
AC_MSG_RESULT([ * postgis SQL files in $PGSQL_SHAREDIR/contrib/postgis-$POSTGIS_MAJOR_VERSION.$POSTGIS_MINOR_VERSION ])
AC_MSG_RESULT([ * postgis executables in $PGSQL_BINDIR ])
AC_MSG_RESULT([------------------------------------------------------------------------])
This is suggestive of some assumptions in the build system, which are
revealed when building in Nix on Darwin: the build fails because the
postgres binary cannot be found in the install prefix specified for
postgis; vis.
cc x -bundle_loader $POSTGIS_PREFIX/bin/postgres
This bundle_loader parameter is only available on Darwin, and this
problem doesn't appear to affect Linux systems.
The solution presented here is to symlink the postgres binary where
PostGIS expects it to be, and then remove it after the build completes.
Upstream switched to a different type of ipset table, whereas we
create ipset in post-start which overrides upstream, and renders
sshguard ineffective.
Remove ipset creation from post-start, and let it get automatically
by upstream script (sshg-fw-ipset) as part of startup
Fixes the following error:
```
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized.
Reinstalling the application may fix this problem.
```
See also #54484 and others.
