[clang] [llvm] [mlir] Enforce single-operand form for llvm.loop.distribute metadata (PR #201077)

[Michael Kruse via cfe-commits]

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Meinersbur wrote:

`opt -passes=verify` runs the verifier multiple times -- before the pass, the pass itself (which is the verifier), after the pass.

However, it seems to be ane established pattern in other verifier tests for some reason, but we should avoid unnecessary work. Please change. 

https://github.com/llvm/llvm-project/pull/201077