[llvm] [SandboxVec] Boilerplate (PR #107431)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

> Hi, I've no idea what to be expected but I noticed that
> 
> ```
> opt -passes=sandbox-vectorizer bbi-98907.ll -o /dev/null
> ```
> 
> crashes with
> 
> ```
> opt: ../lib/SandboxIR/SandboxIR.cpp:2542: llvm::sandboxir::Value *llvm::sandboxir::Context::registerValue(std::unique_ptr<Value> &&): Assertion `Pair.second && "Already exists!"' failed.
> PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.

And this crash goes away with d14a600b1eb
```
[SandboxIR] Implement BlockAddress (#107940)
```

https://github.com/llvm/llvm-project/pull/107431