[clang] [C++20] [Modules] Write comments in C++20 modules' module file (PR #192398)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/14369

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests/78/1365' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-1834392-78-1365.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=1365 GTEST_SHARD_INDEX=78 /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests
--

Script:
--
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests --gtest_filter=LSPTest.CDBConfigIntegration
--
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/LSPClient.cpp:44: Failure
Failed
No result from call after 60 seconds!

/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp:334: Failure
Value of: Client.diagnostics("bar.cpp")
Expected: has a value that has 1 element that diag message (M: "Use of undeclared identifier 'BAR'")
  Actual: (nullopt)

/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/LSPClient.cpp:74: Failure
Failed
Not idle after a minute


/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/LSPClient.cpp:44
Failed
No result from call after 60 seconds!

/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp:334
Value of: Client.diagnostics("bar.cpp")
Expected: has a value that has 1 element that diag message (M: "Use of undeclared identifier 'BAR'")
  Actual: (nullopt)

/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang-tools-extra/clangd/unittests/LSPClient.cpp:74
Failed
Not idle after a minute



********************


```

</details>

https://github.com/llvm/llvm-project/pull/192398