[wide-int] template class generic_wide_int in wide-int.h

[Gerald Pfeifer]

The patch below shaves 404 warnings from stage 1 when bootstrapping
with clang 3.4.1 (i386-unknown-freebsd10.0).

Regardless of whether we agree with that warning in clang, keeping 
things consistent and not using struct once and class in other places 
makes sense.  And I believe Mike was affirmative re a similar patch
last month.

Applied.

Gerald

2014-08-16  Gerald Pfeifer  <ger...@pfeifer.com>

        * wide-int.h (generic_wide_int): Declare as class instead of struct.

Index: wide-int.h
===================================================================
--- wide-int.h  (revision 214062)
+++ wide-int.h  (working copy)
@@ -282,7 +282,7 @@
     wi::int_traits <WI_UNARY_RESULT (T)>::get_binary_result (X, X); \
   HOST_WIDE_INT *VAL = RESULT.write_val ()
 
-template <typename T> struct generic_wide_int;
+template <typename T> class generic_wide_int;
 template <int N> struct fixed_wide_int_storage;
 class wide_int_storage;