[C frontend] Fix construction of TYPE_STUB_DECL

[Jason Merrill]

On 05/21/2015 05:34 PM, Jan Hubicka wrote:
> This would also work, yes.  We can set it into something like "<anonymous>".

> One problem would be that type_with_linkage_p/type_in_anonymous_namespace_p
> would not work on non-C++ types without LTO (because then we do not produce the
> type manglings). I suppose it is not really a problem because only
> place I use them is the devirtualization machinery and that won't get any
> polymorphic types for other languages.

And I don't know whether types from any other languages have linkage 
like C++ times, so that's fine.

> I suppose I can drop type_in_anonymous_namespcae_p in tree.c and make
> mangle_decl to set "anonymous" for those?

Sounds good.

Jason