[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

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git-clang-format --diff eb03279ddcc4bb655021101f0038ece2cec3158a da65e3b79893f64848caca47823ff2ed894ac97d --extensions cpp,h -- clang/test/AST/cxx2c-variadic-friends.cpp clang/test/Parser/cxx2c-variadic-friends.cpp clang/test/SemaCXX/cxx2c-variadic-friends.cpp clang/include/clang/AST/DeclFriend.h clang/include/clang/AST/RecursiveASTVisitor.h clang/include/clang/Sema/Sema.h clang/include/clang/Serialization/ASTBitCodes.h clang/lib/AST/ASTImporter.cpp clang/lib/AST/DeclBase.cpp clang/lib/AST/DeclFriend.cpp clang/lib/AST/DeclPrinter.cpp clang/lib/AST/ODRHash.cpp clang/lib/AST/TextNodeDumper.cpp clang/lib/CodeGen/CGDecl.cpp clang/lib/Frontend/InitPreprocessor.cpp clang/lib/Parse/ParseDeclCXX.cpp clang/lib/Sema/SemaDecl.cpp clang/lib/Sema/SemaDeclCXX.cpp clang/lib/Sema/SemaTemplateInstantiateDecl.cpp clang/lib/Serialization/ASTCommon.cpp clang/lib/Serialization/ASTReaderDecl.cpp clang/lib/Serialization/ASTWriterDecl.cpp clang/tools/libclang/CIndex.cpp
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``````````diff
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index d17e213ea4..bb5822e36c 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -769,7 +769,6 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
   // C++26 features supported in earlier language modes.
   Builder.defineMacro("__cpp_deleted_function", "202403L");
 
-
   if (LangOpts.Char8)
     Builder.defineMacro("__cpp_char8_t", "202207L");
   Builder.defineMacro("__cpp_impl_destroying_delete", "201806L");

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https://github.com/llvm/llvm-project/pull/101448