include "..." looks into relative path first
include <...> doesn't look into relative path at all

The "udf_..." file is in the correct location relative to the "mysql_com.h" file.

Related: #1623950

--- mysql-8.0.11/include/mysql_com.h	2018-04-08 08:44:49.000000000 +0200
+++ mysql-8.0.11/include/mysql_com.h_patched	2018-09-13 13:32:50.018156166 +0200
@@ -1008,7 +1008,7 @@ struct rand_struct {
 };
 
 /* Include the types here so existing UDFs can keep compiling */
-#include <mysql/udf_registration_types.h>
+#include "mysql/udf_registration_types.h"
 
 /**
   @addtogroup group_cs_compresson_constants Constants when using compression




We need to patch the Cmake ABI check file too
--- mysql-8.0.11/include/mysql.h.pp	2018-04-08 08:44:49.000000000 +0200
+++ mysql-8.0.11/include/mysql.h.pp_patched	2018-09-14 13:19:21.763401087 +0200
@@ -173,7 +173,7 @@ struct rand_struct {
   unsigned long seed1, seed2, max_value;
   double max_value_dbl;
 };
-#include <mysql/udf_registration_types.h>
+#include "mysql/udf_registration_types.h"
 enum Item_result {
   INVALID_RESULT = -1,
   STRING_RESULT = 0,