libpq: Fix pkg-config without OpenSSL
Do not add OpenSSL dependencies to libpq pkg-config file if OpenSSL is
not enabled. Oversight in
beff361bc1edc24ee5f8b2073a1e5e4c92ea66eb.
Author: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/
20220331163759.32665-1-fontaine.fabrice%40gmail.com