[patch] Fix two C++ errors in libstdc++. (issue4341041)

[Paolo Carlini]

Hi,
> I think this is a candidate to backport to libstdc++-4.6.1.
>
> exception_ptr.h needs the forward declaration because it's
> included from<typeinfo>  before<typeinfo>  defines std::type_info.
before going ahead with the patch - I'm not at all sure it's enough, for 
<exception> itself for example - I think we should understand why this 
is accepted, note no headers:

namespace std
{
   struct test
   {
     const type_info* fun();
   };
}

Jason?

Paolo.

PS: remember to always post libstdc++ patches to the libstdc++ mailing 
list too