Fix perror fileno namespace (bug 17633)

[Joseph Myers]

On Fri, 21 Nov 2014, Roland McGrath wrote:

> That change is fine, but I'd be more comfortable if we also changed that
> fdopen reference rather than implicitly assuming we'll have the internal
> macro forever.  perror is already using _IO_* calls, so it can just use

If the internal macro is removed (generally or for a particular 
configuration), failures in the linknamespace tests will make it 
immediately obvious that this fdopen call needs to change.

-- 
Joseph S. Myers
joseph@codesourcery.com