pgsql: Mark assorted variables PGDLLIMPORT.

Mark assorted variables PGDLLIMPORT.

This makes life easier for extension authors who wish to support
Windows.

Brian Cloutier, slightly amended by me.

Discussion: http://postgr.es/m/CAJCy68fscdNhmzFPS4kyO00CADkvXvEa-28H-OtENk-pa2OTWw@mail.gmail.com

Branch
------
REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a4116c460299aea7760dc13bd45df5bb5382ed6a

Modified Files
--------------
src/include/access/twophase.h       |  2 +-
src/include/commands/extension.h    |  2 +-
src/include/miscadmin.h             | 10 +++++-----
src/include/pgtime.h                |  2 +-
src/include/postmaster/postmaster.h |  4 ++--
src/include/storage/fd.h            |  2 +-
src/include/storage/proc.h          |  4 ++--
src/include/tcop/dest.h             |  3 ++-
src/include/tcop/tcopprot.h         |  2 +-
src/include/utils/guc.h             |  6 +++---
src/include/utils/snapmgr.h         |  8 ++++----
11 files changed, 23 insertions(+), 22 deletions(-)