As already reported in IRC media-gfx/inkscape-0.92.1-r1 failes to build with gcc 7.3.1. Not sure this is still related to https://bugs.launchpad.net/inkscape/+bug/1660992 as Gentoo has version 0.92.2 in stable and already bumped version to 0.92.3. 

[ebuild N ] media-gfx/inkscape-0.92.1-r1 USE="cdr dbus exif jpeg nls openmp -dia -gnome -imagemagick -inkjar -latex -lcms -postscript -spell -static-libs -visio -wpg" PYTHON_TARGETS="python2_7"

Build log (to big as attachment) >> https://pastebin.com/A497H8F8

Regards