PATCH: fix portability for ext/stdio_filebuf/char/10063-2.cc

[Loren James Rittle]

> Eh! So you read the audit trail of 10063...

My personal opinion would be to stop exposing internal implementation
as extension; however, the users appear to want this one badly.

Here is the conflict, unless stdio_sync_filebuf -> (becomes)
stdio_filebuf; 10063-2.cc is ill-formed as a portable test case.  Now
that we offer the user the ability to create an object with sync
property, the test case should reflect that.  Thus, I dupped the test
case into -3 applied my change; and then disabled buffering in -2.

Regards,
Loren