qemu-option.h include protectors

qemu-option.h has no protection against including it twice.
This patch adds the usual "#ifndef header" bits.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

qemu-config.h

+#ifndef QEMU_CONFIG_H
+#define QEMU_CONFIG_H
+
 extern QemuOptsList qemu_drive_opts;
 extern QemuOptsList qemu_device_opts;
 
 int qemu_set_option(const char *str);
+
+#endif /* QEMU_CONFIG_H */