linux-user: fake /proc/self/auxv

Gtk tries to read /proc/self/auxv to find its auxv table instead of
taking it from its own program memory space.

However, when running with linux-user, we see the host's auxv which
clearly exposes wrong information. so let's instead expose the guest
memory backed auxv tables via /proc/self/auxv as well.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
