compilation failure on windows

storage/perfschema/unittest/pfs_server_stubs.cc

@@ -33,7 +33,7 @@ void compute_digest_md5(const sql_digest_storage *, unsigned char *)
 {
 }
 
-struct sys_var { enum where { AUTO }; };
+class sys_var { public: enum where { AUTO }; };
 void mark_sys_var_value_origin(void *ptr, enum sys_var::where here)
 {
 }