C++: fix ICE with CONST_DECLs

[Mike Stump]

Here is a simple one.  When processing CONST_DECLs after an error, we can ICE.  
This avoid the ICE.

Ok?


2013-06-11  Mike Stump  <mikest...@comcast.net>

        * init.c (constant_value_1): Protect CONST_DECLs better in the
          face of errors.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 44e558e..133a162 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -1988,7 +1988,7 @@ constant_value_1 (tree decl, bool integral_p, bool 
return_aggregate_cst_ok_p)
       init = DECL_INITIAL (decl);
       if (init == error_mark_node)
        {
-         if (DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl))
+         if (VAR_P (decl) && DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl))
            /* Treat the error as a constant to avoid cascading errors on
               excessively recursive template instantiation (c++/9335).  */
            return init;