[llvm] DynamicAPInt: optimize size of structure (PR #97831)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Okay, the results are in, and I'm confused as to why there is a 36% slowdown:

```md
| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./main` | 749.2 ± 25.0 | 720.6 | 794.7 | 1.00 |
| `./patch` | 1015.4 ± 23.5 | 988.3 | 1053.3 | 1.36 ± 0.05 |
```

https://github.com/llvm/llvm-project/pull/97831