A couple of #ifdef changes necessary to use NetBSD's ucontext
structs on sparc64 and arm.

Signed-off-by: Tobias Nygren <tnn@NetBSD.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1425591461-17550-1-git-send-email-tnn@NetBSD.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>