Created attachment 870778 [details] build log. setup: clang profile + native + 03 + lto thin + -glldb -g .
Created attachment 870779 [details] /etc/portage/make.conf
Fixed in 3.5.28-r4 https://github.com/gentoo/gentoo/blob/master/app-text/djvu/files/djvu-3.5.28-drop-register-keyword-clang16.patch