Is there a reason to force installation of corefonts? System-wide settings and aliases may break system fonts (and especially fonts on web page) if those fonts will be installed. corefonts are also not updated anymore (new versions are not provided in the same way), and using old versions is pointless (or at least forcing usage of those fonts). I already used coolreader earlier without corefonts and I don't remeber any problems without them.
commit d0f636c44313da888367144ffebaab6e502e25a9 (HEAD -> master, origin/master, origin/HEAD) Author: Andrey Grozin <grozin@gentoo.org> Date: Thu Aug 31 10:18:12 2017 +0700 app-text/coolreader: removed RDEPEND on corefonts Bug: 629394 Package-Manager: Portage-2.3.6, Repoman-2.3.3