[clang-tools-extra] [clang-doc] Precommit concept tests (PR #144160)

[Paul Kirth via cfe-commits]

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@@ -0,0 +1,37 @@
+// RUN: rm -rf %t && mkdir -p %t
+// RUN: clang-doc --extra-arg -std=c++20 --output=%t --format=json --executor=standalone %s
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ilovepi wrote:

Let’s try to mark it fail with filecheck. If that’s doesn’t work, I’m ok with this. 

https://github.com/llvm/llvm-project/pull/144160