MDEV-36347 UBSAN: plugins.auth_v0100 - runtime error: call to function do_auth_0x0100

through pointer to incorrect function type.

Redoing a new plugin interface for an obsolete protocol was
too much so we just remove the UBSAN testing on the function.

It wasn't possible to just disable funtion-type-mismatch

plugin/auth_examples/auth_0x0100.c

@@ -56,6 +56,10 @@ struct st_mysql_auth
 };
 #endif
 
+/* function-type-mismatch ignore */
+#if defined(__clang__)
+__attribute__((no_sanitize("undefined")))
+#endif
 static int do_auth_0x0100(MYSQL_PLUGIN_VIO *vio, MYSQL_SERVER_AUTH_INFO *info)
 {
   info->password_used= 1;