Silence another gcc 11 warning.

Per buildfarm and local experimentation, bleeding-edge gcc isn't
convinced that the MemSet in reorder_function_arguments() is safe.
Shut it up by adding an explicit check that pronargs isn't negative,
and by changing MemSet to memset.  (It appears that either change is
enough to quiet the warning at -O2, but let's do both to be sure.)

src/backend/optimizer/util/clauses.c

@@ -3805,9 +3805,9 @@ reorder_function_arguments(List *args, HeapTuple func_tuple)
 	int			i;
 
 	Assert(nargsprovided <= pronargs);
-	if (pronargs > FUNC_MAX_ARGS)
+	if (pronargs < 0 || pronargs > FUNC_MAX_ARGS)
 		elog(ERROR, "too many function arguments");
-	MemSet(argarray, 0, pronargs * sizeof(Node *));
+	memset(argarray, 0, pronargs * sizeof(Node *));
 
 	/* Deconstruct the argument list into an array indexed by argnumber */
 	i = 0;