According to the commit message in 8ec569479, we must have all variables
in header files marked with PGDLLIMPORT. In commit d3cc5ffe81 some
variables were moved from launch_backend.c file to several header files.
This adds PGDLLIMPORT to moved variables.
Author: Sofia Kopikova <s.kopikova@postgrespro.ru>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/e0b17014-5319-4dd6-91cd-93d9c8fc9539%40postgrespro.ru