BuildRequires: s/postgresql-devel/libpq-devel/
That's because we moved libpq.so.5 into libpq package. But I had
to add postgresql-server-devel too, even though it shouldn't be
needed. My guess is that the buildsystem configuration tooling
mistakenly checks for server-related headers.
Related: rhbz#1618698, rhbz#1623764