[IA64] fix userspace compile error in gcc_intrin.h

Fixes userspace build errors when linux/ipv6.h is included such as in the
dhcpv6 package under fedora.  Likely causes other userspace build errors as
well.  I found this in akpm's tree from 2.6.18 but could not find any case
of anyone proposing it for the main tree.

Signed-off-by: Doug Chapman <doug.chapman@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>