V3 PATCH: Include libio.h where required

[Benjamin Kosnik]

> That's what I thought, but I saw:
> 
>   #ifdef _GLIBCPP_USE_WCHAR_T
>     typedef _IO_wide_data __c_wfile_type;
>     extern "C" struct __c_libio_codecvt { };
>   #endif 

this is wrong

> So, I assumed that you must have intended to use libio for the
> wide-character bits.

no, I made this file without doing wide bits, so this stuff must have 
been copied by accident. 

> If that can go -- and if we can always make _GLIBCPP_USE_WCHAR_T false
> when c_io_stdio is in use, then we can get rid of my change.  If you
> approve that direction, I'll make the necessary changes, including the
> minor configury bits.

ok, sounds good. (you could make wide character specializations as in 
the c_io_libio file, if you wanted to implement wchar_t functionality 
with standard wide io functions. That's probably best left for later 
though.)

-benjamin