Follow-up to https://github.com/llvm/llvm-project/pull/96932

Adds XFAILed test where LLDB incorrectly infers the alignment of a
derived class whose bases are overlapping due to [[no_unique_address]].
Specifically, the `InferAlignment` code-path of the
`ItaniumRecordLayoutBuilder` assumes that overlapping base offsets imply
a packed structure and thus sets alignment to 1. See discussion in
https://github.com/llvm/llvm-project/pull/93809.

Also adds test where LLDB correctly infers an alignment of `1` when a
packed base class is overlapping with other bases.

Lastly, there were a couple of `alignof` inconsistencies which I
encapsulated in an XFAIL-ed `packed-alignof.cpp`.