pgsql: Clean up some inconsistencies with GUC declarations

Clean up some inconsistencies with GUC declarations

This is similar to 7d25958, and this commit takes care of all the
remaining inconsistencies between the initial value used in the C
variable associated to a GUC and its default value stored in the GUC
tables (as of pg_settings.boot_val).

Some of the initial values of the GUCs updated rely on a compile-time
default.  These are refactored so as the GUC table and its C declaration
use the same values.  This makes everything consistent with other
places, backend_flush_after, bgwriter_flush_after, port,
checkpoint_flush_after doing so already, for example.

Extracted from a larger patch by Peter Smith.  The spots updated in the
modules are from me.

Author: Peter Smith, Michael Paquier
Reviewed-by: Nathan Bossart, Tom Lane, Justin Pryzby
Discussion: https://postgr.es/m/CAHut+PtHE0XSfjjRQ6D4v7+dqzCw=d+1a64ujra4EX8aoc_Z+w@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/d9d873bac67047cfacc9f5ef96ee488f2cb0f1c3

Modified Files
--------------
contrib/auth_delay/auth_delay.c                 |  2 +-
contrib/pg_prewarm/autoprewarm.c                |  2 +-
contrib/pg_stat_statements/pg_stat_statements.c | 11 +++---
contrib/pg_trgm/trgm_op.c                       |  6 +--
contrib/sepgsql/hooks.c                         |  4 +-
src/backend/access/transam/xact.c               |  2 +-
src/backend/access/transam/xlog.c               |  2 +-
src/backend/libpq/be-secure.c                   |  4 +-
src/backend/postmaster/postmaster.c             |  2 +-
src/backend/storage/buffer/bufmgr.c             | 10 ++---
src/backend/storage/ipc/dsm_impl.c              |  2 +-
src/backend/utils/adt/xml.c                     |  4 +-
src/backend/utils/cache/plancache.c             |  2 +-
src/backend/utils/error/elog.c                  |  2 +-
src/backend/utils/init/globals.c                |  4 +-
src/backend/utils/misc/guc_tables.c             | 50 +++++++++++--------------
src/backend/utils/misc/ps_status.c              |  3 +-
src/include/storage/bufmgr.h                    |  9 +++++
src/include/utils/ps_status.h                   |  7 ++++
19 files changed, 70 insertions(+), 58 deletions(-)