osdep: Make qemu_madvise() return ENOSYS on unsupported OSes

osdep: Make qemu_madvise() return ENOSYS on unsupported OSes

Not every OS is capable of madvise() or posix_madvise() even. In
that case, errno should be set to ENOSYS as it reflects the cause
better.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-ID: <b381c23bd8f413f1453a2c1a66e0979beaf27433.1717584048.git.mprivozn@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>