This patch fixes a bug in serial that made it almost impossible for guest
to communicate with devices through host's serial.

OPOST flag in c_oflag enables output processing letting other flags in
c_oflag take effect. Usually in c_oflag ONLCR flag is also set, which
causes crlf to be sent in place of lf. This breaks binary transmissions.
Unsetting OPOST flag turns off any output processing which fixes the bug.

Bug reports related:
https://bugs.launchpad.net/qemu/+bug/1772086
https://bugs.launchpad.net/qemu/+bug/1407813
https://bugs.launchpad.net/qemu/+bug/1715296
also
https://lists.nongnu.org/archive/html/qemu-devel/2006-06/msg00196.htmlSigned-off-by: NPatryk Olszewski <patryk@fala.ehost.pl>
Message-Id: <1527105041-21013-1-git-send-email-patryk@fala.ehost.pl>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>