Ensure that we delete destructors in the right cases. Specifically:

 - variant members with nontrivial destructors make the containing class's
   destructor deleted
 - check for a virtual destructor after checking for overridden methods in the
   base class(es)
 - check for an inaccessible operator delete for a class with a virtual
   destructor.

Do not try to call an anonymous union field's destructor from the destructor of
the containing class.

llvm-svn: 151483