Fix parallel restore of FKs to partitioned tables

When an FK constraint is created, it needs the index on the referenced
table to exist and be valid.  When doing parallel pg_restore and the
referenced table was partitioned, this condition can sometimes not be
met, because pg_dump didn't emit sufficient object dependencies to
ensure so; this means that parallel pg_restore would fail in certain
conditions.  Fix by having pg_dump make the FK constraint object
dependent on the partition attachment objects for the constraint's
referenced index.

This has been broken since f56f8f8da6, so backpatch to Postgres 12.

Discussion: https://postgr.es/m/20191005224333.GA9738@alvherre.pgsql

src/include/fe_utils/simple_list.h

@@ -2,9 +2,9 @@
  *
  * Simple list facilities for frontend code
  *
- * Data structures for simple lists of OIDs and strings.  The support for
- * these is very primitive compared to the backend's List facilities, but
- * it's all we need in, eg, pg_dump.
+ * Data structures for simple lists of OIDs, strings, and pointers.  The
+ * support for these is very primitive compared to the backend's List
+ * facilities, but it's all we need in, eg, pg_dump.
  *
  *
  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
@@ -43,6 +43,17 @@ typedef struct SimpleStringList
 	SimpleStringListCell *tail;
 } SimpleStringList;
 
+typedef struct SimplePtrListCell
+{
+	struct SimplePtrListCell *next;
+	void	   *ptr;
+} SimplePtrListCell;
+
+typedef struct SimplePtrList
+{
+	SimplePtrListCell *head;
+	SimplePtrListCell *tail;
+} SimplePtrList;
 
 extern void simple_oid_list_append(SimpleOidList *list, Oid val);
 extern bool simple_oid_list_member(SimpleOidList *list, Oid val);
@@ -54,4 +65,6 @@ extern void simple_string_list_destroy(SimpleStringList *list);
 
 extern const char *simple_string_list_not_touched(SimpleStringList *list);
 
+extern void simple_ptr_list_append(SimplePtrList *list, void *val);
+
 #endif							/* SIMPLE_LIST_H */