[clang] [clang] Handle trivial_abi attribute for Microsoft ABI. (PR #88857)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The original patch just changed the calling convention for structs explicitly marked trivial_abi.  @rnk wanted to instead introduce the notion of a "trivial-abi-aware" type, i.e. a type that is either trivial_abi, or contains a trivial-abi-aware field/base.  The patch was never updated to address that.

https://github.com/llvm/llvm-project/pull/88857