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

[Paul Kirth via llvm-commits]

ilovepi wrote:

ah, right. I forgot we build things under `utils` that's a much better place for this. 

Overall the patch is much better. Once it's moved to `utils` I think it will be good.  @nikic I seem to recall that we now prefer markdown over `.rst` files. Is that correct? I tried to find documentation for the policy, but I seem to be missing it in my grep/googling. 

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