[clang] [clang] Fix size and alignment of packed sub-byte integer vectors (PR #161796)

[Steffen Larsen via cfe-commits]

steffenlarsen wrote:

> What's the current state of vector bitcasts with new constexpr engine? (ref https://discourse.llvm.org/t/updating-expectations-for-the-new-constexpr-engine/88853). Assuming that codepath exists, please update it and add testcases.

Sorry for the delay! I've tried turning on the new constexpr interpreter in the tests and it does indeed need changes. I got somewhere, but currently it seems like data location and/or data accesses may be off for these sub-byte types. I hope to return to it shortly.

https://github.com/llvm/llvm-project/pull/161796