coroutine-ucontext: Save fake stack for pooled coroutine

coroutine-ucontext: Save fake stack for pooled coroutine

Coroutine may be pooled even after COROUTINE_TERMINATE if
CONFIG_COROUTINE_POOL is enabled and fake stack should be saved in
such a case to keep AddressSanitizerUseAfterReturn working. Even worse,
I'm seeing stack corruption without fake stack being saved.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240117-asan-v2-1-26f9e1ea6e72@daynix.com>
(cherry picked from commit d9945ccda08ef83b09ac7725b6ee2d1959f2c0c0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>