There was https://gitweb.gentoo.org/repo/gentoo.git/commit/media-gfx/nomacs?id=fb989d0d6694b579fe859ea17b1d9d29537d9b11 media-gfx/nomacs: Revision bump for compatibility with exiv2-0.25 And then https://gitweb.gentoo.org/repo/gentoo.git/commit/media-gfx/exiv2?id=a60ac588121fcc5b30afd56c9055aff7c63b5031 media-gfx/exiv2: amd64 stable wrt bug #565826 But there is presently no stable version of nomacs compatible with exiv2-0.25.
Fortunately, the only incompatibility was a removed USE flag so the worst that should have happened is a missed upgrade.
amd64 stable. Closing.