aclocal 1.9.5 is generating the following warning for gtkmm 1.2.9-r2: /usr/share/aclocal/gtk--.m4:10: warning: underquoted definition of AM_PATH_GTKMM
Created attachment 58596 [details, diff] patch fixes the warning
These are harmless warnings for unmaintained old versions and patching would just be a lot of effort for no gain.