graphics/hugin: prepare for exiv2-0.27

Import gentoo's fix to build against graphics/exiv2 0.27:
https://gitweb.gentoo.org/repo/gentoo.git/diff/media-gfx/hugin/files/hugin-2018.0.0-exiv2-0.27.patch?id=450cbf95fae0141740b2c9f74265220651ee8863

PR: 235943