[C frontend] Fix construction of TYPE_STUB_DECL

[Jan Hubicka]

Hi,
TREE_PUBLIC of TYPE_DECL is defined to say if the type is public:
/* In a VAR_DECL, FUNCTION_DECL, NAMESPACE_DECL or TYPE_DECL,                   
   nonzero means name is to be accessible from outside this translation unit.   
   In an IDENTIFIER_NODE, nonzero means an external declaration                 
   accessible from outside this translation unit was previously seen            
   for this name in an inner scope.  */                                         
#define TREE_PUBLIC(NODE) ((NODE)->base.public_flag)                            

This is properly honored by C++ FE but other FEs are bit random, which in turn
confuses type_in_anonymous_namespace_p predicate that leads to flase poistives
on type mismatch warnings.  I used to be able to get around by checking only
C++ types at LTO time, but with type checking in lto-symtab I can not, because
I do want to compare type compatibility cross translation units and cross languages
and we have no reliable way to say what type originated as C++ and what did not.

This fixed TYPE_STUB_DECl construction in C frontend. I will check other
FEs separately. I can also add way to recognize C++ types, but I think it is
good idea to make type representation consistent across FEs.

Bootstrapped/regtested x86_64-linux, OK?

Honza

	* c-decl.c (pushtag): Declare type as public.
Index: c/c-decl.c
===================================================================
--- c/c-decl.c	(revision 222981)
+++ c/c-decl.c	(working copy)
@@ -1563,6 +1563,7 @@ pushtag (location_t loc, tree name, tree
 
   TYPE_STUB_DECL (type) = pushdecl (build_decl (loc,
 						TYPE_DECL, NULL_TREE, type));
+  TREE_PUBLIC (TYPE_STUB_DECL (type)) = 1;
 
   /* An approximation for now, so we can tell this is a function-scope tag.
      This will be updated in pop_scope.  */