[compiler-rt] [libcxx] [llvm] [clang] [flang] [libc] [clang-tools-extra] [libc++] Implement LWG3940: std::expected<void, E>::value() also needs E to be copy constructible (PR #71819)

[Mark de Wever via cfe-commits]

https://github.com/mordante edited https://github.com/llvm/llvm-project/pull/71819