sql_acl.cc does not compile with WITH_VALGRIND with gcc 8.0

Class Sql_alloc has a constructor when HAVE_valgrind is enabled:

class Sql_alloc

{

public:

 ...

#ifdef HAVE_valgrind

  bool dummy_for_valgrind;

  inline Sql_alloc() :dummy_for_valgrind(0) {}

#endif

};

so gcc-8.0 does not like when bzero is done over Sql_alloc descendants.

sql_acl.cc has some such classes:

• ACL_ACCESS
• ACL_USER_BASE
• ACL_USER
  that derive from Sql_alloc and are used with bzero.