[clang] [Clang] Verify data layout consistency (PR #144720)

[John McCall via cfe-commits]

rjmccall wrote:

So, devil's advocate: do we actually care about IR data layout alignments? Clang should be putting explicit alignments on everything in the IR. And, I mean, I can certainly imagine that a target might end up in an impossible situation for terrible historical reasons, because e.g. it has an `int128_t` with 8-byte alignment but an `__int128_t` with 16-byte alignment.

https://github.com/llvm/llvm-project/pull/144720