Build failure on 32 bit freebsd

I am not exactly what you need to fully debug this, but I have attached the generated [bindings.rs](https://github.com/user-attachments/files/30427238/bindings.rs.txt).

The error is:
```
error[E0080]: attempt to compute `16_usize - 20_usize`, which would overflow
--> /wrkdirs/usr/ports/net-im/libsignal/work/target/release/build/boring-sys-a373168ed8011d63/out/bindings.rs:4907:31
|
4907 | ["Size of __max_align_t"][::std::mem::size_of::<__max_align_t>() - 20usize];
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `generated::_` failed here
```