All backend-side variables should be marked with PGDLLIMPORT, as per
policy introduced in 8ec569479f. aafc05de1bf5 has forgotten
MyClientSocket, and 05c3980e7f47 LoadedSSL.
These can be spotted with a command like this one (be careful of not
switching __pg_log_level):
src/tools/mark_pgdllimport.pl $(git ls-files src/include/)
Reported-by: Peter Eisentraut
Discussion: https://postgr.es/m/ZhzkRzrkKhbeQMRm@paquier.xyz
768ceeeaa1