[clang] [clang][Sema] Propagate `volatile` during derived-to-base conversion (PR #127824)

[Aaron Ballman via cfe-commits]

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+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -ast-dump %s | FileCheck %s
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AaronBallman wrote:

Should we also have a CodeGen test showing that we do a `store/load volatile`?

https://github.com/llvm/llvm-project/pull/127824