Because app-crypt/pinentry can now provide a graphical frontend with USE=qt5 (in addition to USE=qt4 and USE=gtk), please allow this as an additional provider in the || () dep for USE=crypt. Not all versions of app-crypt/pinentry have provided the "qt5" USE flag, so the dependency should be on "app-crypt/pinentry[qt5(-)]".
commit 8cf3d9b748b1920eeb0b758dbde0d25df1c87ad8 Author: Ian Stakenvicius <axs@gentoo.org> Date: Mon May 16 12:45:09 2016 -0400 mail-client/thunderbird: allow pinentry[qt5] Bug: https://bugs.gentoo.org/583134 Package-Manager: portage-2.2.28