* cp-tree.h (DECL_VAR_MARKED_P): Remove.
(DECL_ANON_UNION_VAR_P): New macro.
* class.c (fixed_type_or_null): Tidy. Use a hash table, rather
than DECL_VAR_MARKED_P, to keep track of which variables we have
seen.
* decl.c (redeclaration_error_message): Complain about redeclaring
anonymous union members at namespace scope.
* decl2.c (build_anon_union_vars): Set DECL_ANON_UNION_VAR_P.
* g++.dg/lookup/anon6.C: New test.