Fix Postgres linking on older CMake
Fix Postgres linking on older CMake

(see https://github.com/minetest/minetest/commit/998e4820c982c0ea9d257c15f93f1f21d85d6327)

minetest/minetestmapper,minetest/minetestmapper,minetest/minetestmapper,minetest/minetestmapper