[clang] [clang] Use different memory layout type for _BitInt(N) in LLVM IR (PR #91364)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

> Mariya, would you mind looking into setting this properly on the truncates we're doing here? It'd be fine to do that as a follow-up; no need to hold up this PR for it. You'll need some kind of target hook to tell us whether to set it or not. Probably that ought to go in the Basic TargetInfo just so all of the target-specific ABI configuration is done in one place.

Sure.

https://github.com/llvm/llvm-project/pull/91364