[libstdc++] Don't access fpos_t.__state on uClibc w/o wchar support

[Gabriel Dos Reis]

Pétur Runólfsson <peturr02@ru.is> writes:

| Gabriel Dos Reis wrote:
| > | This won't work because fpos<mbstate_t> is also used for narrow streams.
| > 
| > then we've get a design problem then.
| 
| This is required by the standard (char_traits<char>::pos_type is
| streampos which is fpos<mbstate_t>), so there is not much that can
| be done about it.

I was under the impression that 27.2/10

  This synopsis suggests a circularity between streampos and
  char_traits<char>. An implementation can avoid this circularity by
  substituting equivalent types.

meant something.  But further type-chasing seems to show gratuitous
abstraction.  groumph.

Thanks,

-- Gaby