[llvm] [Support] Remove AlignedCharArrayUnion from Expected and ErrorOr, NFCI. (PR #127407)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie commented:

Could you remove the reinterpret_casts on these members that are now redundant as well?

https://github.com/llvm/llvm-project/pull/127407