bug#72934: lxc fails to build

[Jakob Kirsch]

The error message is:

```
mount_utils.c: In function ‘create_detached_idmapped_mount’:
mount_utils.c:297:29: error: passing argument 4 of ‘mount_setattr’ from 
incompatible pointer type [-Werror=incompatible-pointer-types]
 297 |                             &attr, sizeof(attr));
     |                             ^~~~~
     |                             |
     |                             struct lxc_mount_attr *
In file included from mount_utils.c:9:
/gnu/store/zvlp3n8iwa1svxmwv4q22pv1pb1c9pjq-glibc-2.39/include/sys/mount.h:320:46: 
note: expected ‘struct mount_attr *’ but argument is of type ‘struct 
lxc_mount_attr *’
 320 |                           struct mount_attr *__uattr, size_t 
__usize)
     |                           ~~~~~~~~~~~~~~~~~~~^~~~~~~
mount_utils.c: In function ‘__fd_bind_mount’:
mount_utils.c:380:37: error: passing argument 4 of ‘mount_setattr’ from 
incompatible pointer type [-Werror=incompatible-pointer-types]
 380 |                                     &attr, sizeof(attr));
     |                                     ^~~~~
     |                                     |
     |                                     struct lxc_mount_attr *
In file included from mount_utils.c:9:
/gnu/store/zvlp3n8iwa1svxmwv4q22pv1pb1c9pjq-glibc-2.39/include/sys/mount.h:320:46: 
note: expected ‘struct mount_attr *’ but argument is of type ‘struct 
lxc_mount_attr *’
 320 |                           struct mount_attr *__uattr, size_t 
__usize)
```