Gentoo's Bugzilla –
Attachment 749814 Details for
Bug 822615app-doc/doxygen-1.9.2: In file included from /var/tmp/portage/app-doc/doxygen-1.9.2/work/doxygen-1.9.2/src/constexp.l:29: /var/tmp/portage/app-doc/doxygen-1.9.2/work/doxygen-1.9.2/src/constexp.h:19:10: fatal error: 'string' file not found