[llvm-project] Replace submitted changes with proper backports

Author: hahnjo

interpreter/llvm-project/clang/docs/Modules.rst

@@ -573,6 +573,9 @@ cplusplus14
 cplusplus17
   C++17 support is available.
 
+cplusplus20
+  C++20 support is available.
+
 c99
   C99 support is available.
 

interpreter/llvm-project/clang/lib/AST/ExprConstant.cpp

@@ -15404,6 +15404,15 @@ bool Expr::EvaluateAsInitializer(APValue &Value, const ASTContext &Ctx,
     LVal.set(VD);
 
     {
+      // C++23 [intro.execution]/p5
+      // A full-expression is ... an init-declarator ([dcl.decl]) or a
+      // mem-initializer.
+      // So we need to make sure temporary objects are destroyed after having
+      // evaluated the expression (per C++23 [class.temporary]/p4).
+      //
+      // FIXME: Otherwise this may break test/Modules/pr68702.cpp because the
+      // serialization code calls ParmVarDecl::getDefaultArg() which strips the
+      // outermost FullExpr, such as ExprWithCleanups.
       FullExpressionRAII Scope(Info);
       if (!EvaluateInPlace(Value, Info, LVal, this,
                            /*AllowNonLiteralTypes=*/true) ||

interpreter/llvm-project/llvm-project.tag

@@ -1 +1 @@
-ROOT-llvm16-20231130-01
+ROOT-llvm16-20240115-01