[Bug libstdc++/104299] Doc: stdio is not the only option in --enable-cstdio=XXX

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104299

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=110574
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-07-06

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
stdio_posix is a synonym of stdio, but we should document stdio_pure