[clang] [CIR][AArch64] Upstream narrowing-addition NEON builtins (PR #204989)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space approved this pull request.

LGTM, thank you!

This one has been quite tricky, thank you for seeing it through! Please wait till tomorrow before landing. Just in case @E00N777 (or other reviewers) would like to take another look.

https://github.com/llvm/llvm-project/pull/204989