PR 56981 Improve unbuffered performance on special files.

PR 56981 Improve unbuffered performance on special files.

2013-04-29  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/56981
        * io/transfer.c (next_record_w_unf): First fix head marker, then
        write tail.
        (next_record): Call flush_if_unbuffered.
        * io/unix.c (struct unix_stream): Add field unbuffered.
        (flush_if_unbuffered): New function.
        (fd_to_stream): New argument.
        (open_external): Fix fd_to_stream call.
        (input_stream): Likewise.
        (output_stream): Likewise.
        (error_stream): Likewise.
        * io/unix.h (flush_if_unbuffered): New prototype.

From-SVN: r198390