```
`#pragma pack(1)` prevents aligning the struct and its members to their
required alignment. This can result in code that performs non-aligned
reads and writes to integers and pointers, which is problematic on some
architectures.
It also triggers UBsan — see
https://github.com/bitcoin/bitcoin/pull/17156#issuecomment-543123631
and #17510.
```
Backport of core PR17708.