/usr/include/postgresql/8.4/server/libpq/ is in postgresql-server-dev-8.4 8.4.11-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/postgresql/8.4/server/libpq/auth.h
/usr/include/postgresql/8.4/server/libpq/be-fsstubs.h
/usr/include/postgresql/8.4/server/libpq/crypt.h
/usr/include/postgresql/8.4/server/libpq/hba.h
/usr/include/postgresql/8.4/server/libpq/ip.h
/usr/include/postgresql/8.4/server/libpq/libpq-be.h
/usr/include/postgresql/8.4/server/libpq/libpq-fs.h
/usr/include/postgresql/8.4/server/libpq/libpq.h
/usr/include/postgresql/8.4/server/libpq/md5.h
/usr/include/postgresql/8.4/server/libpq/pqcomm.h
/usr/include/postgresql/8.4/server/libpq/pqformat.h
/usr/include/postgresql/8.4/server/libpq/pqsignal.h