Comment 7 for bug 1649530

OK. Let's take another approach. Could you locate your icontheme.h file which is part of gtkmm where the unrecognized function should be defined. It should be in a path similar to this: /usr/include/gtkmm-3.0/gtkmm

in that file look for a line like this:
IconInfo lookup_icon(const Glib::ustring& icon_name, int size, IconLookupFlags flags = (IconLookupFlags)0) const;