Add missing postgres.h includes

After sorting includes in the previous commit some files were now
invalid because they were not including postgres.h

src/backend/distributed/planner/intermediate_result_pruning.c

@@ -12,6 +12,8 @@
  *-------------------------------------------------------------------------
  */
 
+#include "postgres.h"
+
 #include "common/hashfn.h"
 #include "utils/builtins.h"
 

src/backend/distributed/utils/replication_origin_session_utils.c

@@ -8,6 +8,8 @@
  *-------------------------------------------------------------------------
  */
 
+#include "postgres.h"
+
 #include "miscadmin.h"
 
 #include "utils/builtins.h"