bugfix: -fno-strict-aliasing, because tun.c breaks the rules.

(What it does is: fills in 'struct sockaddr' fields of 'struct
rtentry' by casting to 'struct sockaddr_in' pointers and accessing
through those.  A more intrusive change would be to construct the
sockaddr_in in another object and then memcpy it into place, which
would achieve the same effect without (AFAIK) breaching C's aliasing
rules.)

Signed-off-by: Richard Kettlewell <richard@greenend.org.uk>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>