[clang] Implement [[msvc::no_unique_address]] (PR #65675)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Added @erichkeane as attributes code owner, and @efriedma-quic and @rjmccall as codegen code owners.

The attributes changes look good to me. The codegen changes seem reasonable, but are a bit outside my area of expertise for me to feel comfortable signing off on. The only thing I did spot was that this should come with a change to the release notes so users know about the new functionality and its stability guarantees.

https://github.com/llvm/llvm-project/pull/65675