[clang] [llvm] [mlir] Enforce single-operand form for llvm.loop.vectorize.predicate metadata (PR #213902)

[Michael Kruse via llvm-commits]

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Meinersbur wrote:

```suggestion
#### '`llvm.loop.vectorize.predicate.enable`' and '`llvm.loop.vectorize.predicate.disable`' Metadata
```

https://github.com/llvm/llvm-project/pull/213902