[clang] Add code completion for C++20 keywords. (PR #107982)

[via cfe-commits]

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@@ -1837,6 +1837,10 @@ static void AddTypeSpecifierResults(const LangOptions &LangOpts,
       Builder.AddChunk(CodeCompletionString::CK_RightParen);
       Results.AddResult(Result(Builder.TakeString()));
     }
+
+    if (LangOpts.CPlusPlus20) {
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cor3ntin wrote:

That can also be enabled by `LangOpts.Char8`

https://github.com/llvm/llvm-project/pull/107982