pgsql: Fix missing fsync of SLRU directories.

Fix missing fsync of SLRU directories.

Harmonize behavior by moving reponsibility for fsyncing directories down
into slru.c.  In 10 and later, only the multixact directories were
missed (see commit 1b02be21), and in older branches all SLRUs were
missed.

Back-patch to all supported releases.

Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CA%2BhUKGLtsTUOScnNoSMZ-2ZLv%2BwGh01J6kAo_DM8mTRq1sKdSQ%40mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/aca74843e40f43d0cceffd314aec6aa6f80e83d5

Modified Files
--------------
src/backend/access/transam/clog.c      | 7 -------
src/backend/access/transam/commit_ts.c | 6 ------
src/backend/access/transam/slru.c      | 4 ++++
3 files changed, 4 insertions(+), 13 deletions(-)