tools/virtio: add struct cpumask to cpumask.h

Add struct cpumask stub used by virtio_config.h.

Created using Cursor CLI.

Message-ID: <eacf56399ba220513ebcd610f4a5115dc768db80.1764873799.git.mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Author: mstsirkin

tools/virtio/linux/cpumask.h

@@ -4,4 +4,8 @@
 
 #include <linux/kernel.h>
 
+struct cpumask {
+	unsigned long bits[1];
+};
+
 #endif /* _LINUX_CPUMASK_H */