checking for GDKMM... no configure: error: Package requirements (giomm-2.4 >= 2.49.1 pangomm-1.4 >= 2.38.2 gtk+-3.0 >= 3.22.0 cairomm-1.0 >= 1.12.0 gdk-pixbuf-2.0 >= 2.35.5) were not met: Requested 'gtk+-3.0 >= 3.22.0' but version of GTK+ is 3.20.9 Consider adjusting the PKG_CONFIG_PATH environment variable if you installed software in a non-standard prefix. Alternatively, you may set the environment variables GDKMM_CFLAGS and GDKMM_LIBS to avoid the need to call pkg-config. See the pkg-config man page for more details. Fix would be s/x11-libs/gtk+-3.20.0:3/x11-libs/gtk+-3.22.5
Thanks, 3.22.0 should be sufficient as per upstream check commit 523c39ddd01f5d8aaeb5d6b3147c4f1746b9b2e3 Author: Mart Raudsepp <leio@gentoo.org> Date: Sun Mar 19 01:04:47 2017 +0200 dev-cpp/gtkmm: fix gtk+:3 minimum dependency Gentoo-bug: 612622 Package-Manager: Portage-2.3.4, Repoman-2.3.1