10.3: gcc-8.0 produces lots of -Wclass-memaccess warnings in Table_scope_and_contents_source_st

• Note: the problem is repeatable with 10.2 and earlier versions as well. But in 10.2 and earlier we don't have Vers_parse_info, so it can be fixed by a simpler (but not future proof) patch, e.g. casting "this" to void*. Using cast to void is dangerous though, so it should be avoided in 10.3+.
• Note: 10.2 and earlier versions will be fixed under terms of a separate MDEV

gcc-8.0 has a new warning when a class or struct with a constructor is bzero'd.

A lot of warnings if this kind are generated by this method:

struct Table_scope_and_contents_source_st

..

  void init()

  {

    bzero(this, sizeof(*this));

  }

..

This structure has non-trivial members:

• SQL_I_List<TABLE_LIST> merge_list;
• Vers_parse_info vers_info;

which have constructors.

So bzero'ing is not indeed logically correct. Moveover, the constructor of SQL_I_LIST does more than just bzero.

This should be fixed.