[clang] [CIR][AArch64] Upstream addition and polynomial-addition NEON builtins (PR #202005)

[Andrzej Warzyński via cfe-commits]

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

Great, thank you!

Before landing this, could you move the new tests to neon/add.c instead of neon/intrinsics.c? The latter is already too large and we should split it at some point.

https://github.com/llvm/llvm-project/pull/202005