See attached build log.
(Please do not complain about the need for looking at the build log until you can provide an easy way to open bugs with the correct data picked out of a tinderbox log. Thanks.)
Created attachment 250509 [details]
dev-dpp/libpqpp should probably be removed from the tree in favour of dev-libs/libpqxx rather than fixing it.
dev-dpp/libpqpp hasn't been updated in some years while dev-libs/libpqxx has been updated recently.
Removed from tree.