[llvm] [Support] Replace deprecated std::aligned_union, NFCI. (PR #127417)

[Jonas Hahnfeld via llvm-commits]

hahnjo wrote:

@jplehr I played a bit with Compiler Explorer and it seems the problem is `alignas(Ts...)`, I couldn't get it to work with any parameter pack. But `static constexpr std::size_t Align = std::max({alignof(T), alignof(Ts)...});` seems to work (https://godbolt.org/z/Mf3hzezPa) and should be fine because it's all power-of-two's. Do you have easy access to the bot / a similar machine? If not, I can commit and we revert if it still doesn't work...

https://github.com/llvm/llvm-project/pull/127417