pgsql: Fix buildfarm failures from 2af07e2f74.

Fix buildfarm failures from 2af07e2f74.

Use GUC_ACTION_SAVE rather than GUC_ACTION_SET, necessary for working
with parallel query.

Now that the call requires more arguments, wrap the call in a new
function to avoid code duplication and offer a place for a comment.

Discussion: https://postgr.es/m/E1rhJpO-0027Wf-9L@gemulon.postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/59825d16399699e2f99016b9add46cb2d4916f82

Modified Files
--------------
contrib/amcheck/t/004_verify_nbtree_unique.pl | 45 +++++++++++----------------
contrib/amcheck/verify_nbtree.c | 3 +-
src/backend/access/brin/brin.c | 3 +-
src/backend/catalog/index.c | 13 +++-----
src/backend/commands/analyze.c | 3 +-
src/backend/commands/cluster.c | 3 +-
src/backend/commands/indexcmds.c | 10 ++----
src/backend/commands/matview.c | 3 +-
src/backend/commands/vacuum.c | 3 +-
src/backend/utils/misc/guc.c | 19 +++++++++++
src/include/utils/guc.h | 7 +----
11 files changed, 52 insertions(+), 60 deletions(-)