Fix pkg-config files for static linking
Since
ea53100d5 (PostgreSQL 12), the shipped pkg-config files have
been broken for statically linking libpq because libpgcommon and
libpgport are missing. This patch adds those two missing private
dependencies (in a non-hardcoded way).
Reported-by: Filip Gospodinov <f@gospodinov.ch>
Discussion: https://www.postgresql.org/message-id/flat/
c7108bde-e051-11d5-a234-
99beec01ce2a@gospodinov.ch