Stabilize postgres_fdw tests on 32-bit machines

cac169d68 adjusted DEFAULT_FDW_TUPLE_COST and that seems to have caused
a test to become unstable on 32-bit machines.

4b14e1871 tried to fix this as originally the plan was flipping between
a Nested Loop and Hash Join.  That commit forced the Nested Loop, but
there's still flexibility to push or not push the sort to the remote
server and 32-bit seems to prefer to push and on 64-bit, the costs
prefer not to.

Here let's just turn off enable_sort to significantly encourage the sort
to take place on the remote server.

Reported-by: Michael Paquier, Richard Guo
Discussion: https://postgr.es/m/ZUM2IhA8X2lrG50K@paquier.xyz

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -4019,27 +4019,25 @@ EXECUTE st1(101, 101);
 (1 row)
 
 SET enable_hashjoin TO off;
+SET enable_sort TO off;
 -- subquery using stable function (can't be sent to remote)
 PREPARE st2(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c4) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st2(10, 20);
-                                                QUERY PLAN                                                
-----------------------------------------------------------------------------------------------------------
- Sort
+                                                            QUERY PLAN                                                            
+----------------------------------------------------------------------------------------------------------------------------------
+ Nested Loop Semi Join
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
+   Join Filter: (t2.c3 = t1.c3)
+   ->  Foreign Scan on public.ft1 t1
          Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
+         Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20)) ORDER BY "C 1" ASC NULLS LAST
+   ->  Materialize
+         Output: t2.c3
+         ->  Foreign Scan on public.ft2 t2
                Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Filter: (date(t2.c4) = '01-17-1970'::date)
-                     Remote SQL: SELECT c3, c4 FROM "S 1"."T 1" WHERE (("C 1" > 10))
-(15 rows)
+               Filter: (date(t2.c4) = '01-17-1970'::date)
+               Remote SQL: SELECT c3, c4 FROM "S 1"."T 1" WHERE (("C 1" > 10))
+(12 rows)
 
 EXECUTE st2(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4054,6 +4052,7 @@ EXECUTE st2(101, 121);
 (1 row)
 
 RESET enable_hashjoin;
+RESET enable_sort;
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -1123,12 +1123,14 @@ EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st1(1, 2);
 EXECUTE st1(1, 1);
 EXECUTE st1(101, 101);
 SET enable_hashjoin TO off;
+SET enable_sort TO off;
 -- subquery using stable function (can't be sent to remote)
 PREPARE st2(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c4) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st2(10, 20);
 EXECUTE st2(10, 20);
 EXECUTE st2(101, 121);
 RESET enable_hashjoin;
+RESET enable_sort;
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);