pgsql: Do not rely on pgstat.h to indirectly include storage/ headers.

Do not rely on pgstat.h to indirectly include storage/ headers.

An upcoming patch might remove the (now indirect) proc.h
include (which in turn includes other headers), and it's cleaner for
the modified files to include their dependencies directly anyway...

Discussion: https://postgr.es/m/20210402194458.2vu324hkk2djq6ce@alap3.anarazel.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/1d9c5d0ce2dcac05850401cf266a9df10a68de49

Modified Files
--------------
contrib/pg_stat_statements/pg_stat_statements.c | 2 ++
src/backend/postmaster/pgarch.c                 | 2 ++
src/backend/postmaster/pgstat.c                 | 1 +
src/backend/replication/walreceiver.c           | 1 +
src/backend/storage/lmgr/lmgr.c                 | 1 +
src/backend/utils/adt/misc.c                    | 1 +
6 files changed, 8 insertions(+)