src: conditionally exclude cfmakeraw/termios.h on WIN32

src: conditionally exclude cfmakeraw/termios.h on WIN32

The GNULIB termios module ensures termios.h exists (but
is none the less empty) when building for Windows. We
already exclude usage of the functions that would exist
in a real termios.h, so having an empty termios.h is
not especially useful.

It is simpler to just put all use of termios.h related
functions behind a "#ifndef WIN32" conditional.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>