[llvm] [SimplifyCFG]: Switch on umin replaces default (PR #164097)

[via llvm-commits]

https://github.com/dianqk approved this pull request.

LGTM, but we usually introduce a `Changed` variable to do this. For example:

```
bool Changed = false;
if (DoSomethingA())
  Changed = true;
if (DoSomethingB())
  Changed = true;
return Changed;
```

https://github.com/llvm/llvm-project/pull/164097