Makefile uses Linux-specific option --force

[simonjwright]

This line in Makefile.in

ln -s ${libdir} ${DESTDIR}${datadir}/examples/gtkada --force

uses the Linux-specific option --force (at the end of the command, too, which is highly unusual).
This option isn’t available on macOS: please change to the more standard

ln -s -f ${libdir} ${DESTDIR}${datadir}/examples/gtkada