miri: add some chance to reuse addresses of previously freed allocations
The hope is that this can help us find ABA issues.
Unfortunately this needs rustc changes so I can't easily run the regular benchmark suite. I used `src/tools/miri/tests/pass/float_nan.rs` as a substitute:
```
Before:
Benchmark 1: ./x.py run miri --stage 0 --args src/tools/miri/tests/pass/float_nan.rs --args --edition=2021
Time (mean ± σ): 9.570 s ± 0.013 s [User: 9.279 s, System: 0.290 s]
Range (min … max): 9.561 s … 9.579 s 2 runs
After:
Benchmark 1: ./x.py run miri --stage 0 --args src/tools/miri/tests/pass/float_nan.rs --args --edition=2021
Time (mean ± σ): 9.698 s ± 0.046 s [User: 9.413 s, System: 0.279 s]
Range (min … max): 9.666 s … 9.731 s 2 runs
```
That's a ~1.3% slowdown, which seems fine to me. I have seen a lot of noise in this style of benchmarking so I don't quite trust this anyway; we can make further experiments in the Miri repo after this migrated there.
r? `@oli-obk`
9ce37dc729