[clang-tools-extra] [llvm] [llvm] add tool to verify mustache library (PR #111487)

[via llvm-commits]

PeterChou1 wrote:

> Please call this llvm-mustache-spec -- let's try to avoid polluting the global namespace with niche tools.
> 
> I also wonder whether this shouldn't be a util rather than tool -- this is purely for internal use, right?

Yes this a utility purely for internal use, I did not realize there was already a utils folder

https://github.com/llvm/llvm-project/pull/111487