Per bug 1174373 comment 13, IMHO RHEL7 gtkmm30 should be rebased to 3.14.0: 1) Not having gtkmm30 up to 3.14 limits the potential of adding other GTKmm-based software (particularly gtksourceviewmm3/goocanvasmm2/glom) to EPEL to the GNOME 3.8 versions, despite gtk3 and gtksourceview3 themselves being 3.14. 2) Any future rebuild of gtkmm30-3.8.1 will FTBFS with gtk3-3.14.x.
*** This bug has been marked as a duplicate of bug 1386982 ***