Use the POSIX-specified stack_t type as the argument to sigaltstack()
rather than the legacy struct sigaltstack. This allows us to compile
on MacOSX with --with-coroutine=sigaltstack.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>