[llvm] [llvm] Add a tool to check mustache compliance against the public spec (PR #142813)

[Nikita Popov via llvm-commits]

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+llvm-test-mustache-spec - LLVM tool to test Mustache Compliance Library
+=========================================================================
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nikic wrote:

```suggestion
=======================================================================
```

https://github.com/llvm/llvm-project/pull/142813