* class.c (finish_struct_1): Add vbase fields earlier. Set
CLASSTYPE_SIZE of an empty base to 0. Types with bases can be empty.
* search.c (dfs_check_overlap, dfs_no_overlap_yet): New fns.
(types_overlap_p): New fn.
* tree.c (avoid_overlap): New fn.
(build_base_fields): Use it to avoid overlapping empty bases.
* cp-tree.h, decl2.c, lang-options.h: Add -fnew-abi.
From-SVN: r18978
