Fail when weight set and set_identifier not set

Resolves https://github.com/hashicorp/terraform/issues/5776

builtin/providers/aws/resource_aws_route53_record.go

@@ -468,6 +468,9 @@ func resourceAwsRoute53RecordBuildSet(d *schema.ResourceData, zoneName string) (
 
 	w := d.Get("weight").(int)
 	if w > -1 {
+		if _, ok := d.GetOk("set_identifier"); !ok {
+			return nil, fmt.Errorf(`provider.aws: aws_route53_record: %s: "set_identifier": required field is not set when "weight" is set`, d.Get("name").(string))
+		}
 		rec.Weight = aws.Int64(int64(w))
 	}