Packed&aligned structs?

Here they explain the need for repr(C) structs that are both aligned and packed:
https://immunant.com/blog/2020/06/kernel_modules/

Their solution:
```rust
#[repr(C, align(64))]
pub struct xregs_state(pub xregs_state_Inner);
#[repr(C, packed)]
pub struct xregs_state_Inner {
  // ...
}
```

Perhaps it's worth supporting this directly.