libstdc++ v3 wants more libio functions now

[Richard Kenner]

    I am just fixing the code in GNAT for interfacing with C wide
    characters.  GNAT assumed that C wchar_t was a 16-bit quantity, but we
    were notified by a user that this actually was defined as Integer'Size
    in GCC. If this definition may be changed to 16-bit anytime soon, I'd
    like to know so I can avoid double changes.

On some machines it's 16 bits, on others the integer size.  Use
WCHAR_TYPE_SIZE.