As POSIX states [1] a freopen call should first flush the stream as if by a
call fflush. C99 (n1256) and C11 (n1570) only states the function should
first close any file associated with the specific stream. Although current
implementation only follow C specification, current BSD and other libc
implementation (musl) are in sync with POSIX and fflush the stream.
This patch change freopen{64} to fflush the stream before actually reopening
it (or returning if the stream does not support reopen). It also changes the
Linux implementation to avoid a dynamic allocation on 'fd_to_filename'.
Checked on x86_64-linux-gnu.
[BZ #21037]
* libio/Makefile (tests): Add tst-memstream4 and tst-wmemstream4.
* libio/freopen.c (freopen): Sync stream before reopen and adjust to
new fd_to_filename interface.
* libio/freopen64.c (freopen64): Likewise.
* libio/tst-memstream.h: New file.
* libio/tst-memstream4.c: Likewise.
* libio/tst-wmemstream4.c: Likewise.
* sysdeps/generic/fd_to_filename.h (fd_to_filename): Change signature.
* sysdeps/unix/sysv/linux/fd_to_filename.h (fd_to_filename): Likewise
and remove internal dynamic allocation.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/
