Attempt to fix compiler warning.

Per a report from Tom Lane, newer versions of gcc apparently think
that partexprs_item_saved can be used uninitialized.  Try to convince
them otherwise.

src/backend/catalog/partition.c

@@ -1558,6 +1558,7 @@ get_qual_for_range(PartitionKey key, PartitionBoundSpec *spec)
 	 */
 	i = 0;
 	partexprs_item = list_head(key->partexprs);
+	partexprs_item_saved = partexprs_item;		/* placate compiler */
 	forboth(cell1, spec->lowerdatums, cell2, spec->upperdatums)
 	{
 		EState	   *estate;