Two minor fixes:  1.  Put integral_constant conversion to integral in even without constexpr support.  2.  Add ios_base to <iosfwd>.  The latter is being tracked by LWG 2026.

llvm-svn: 123080
diff --git a/libcxx/include/iosfwd b/libcxx/include/iosfwd
index 1f9fe3b..0e5c683 100644
--- a/libcxx/include/iosfwd
+++ b/libcxx/include/iosfwd
@@ -92,6 +92,8 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+class ios_base;
+
 template<class _CharT>  struct _LIBCPP_VISIBLE char_traits;
 template<class _Tp>     class _LIBCPP_VISIBLE allocator;