[clang] [CIR][AArch64] Upstream widening-addition NEON builtins (PR #204285)

[Jiahao Guo via cfe-commits]

https://github.com/E00N777 commented:

Thank you very much for your contribution.

 However, I think there is some overlap between our work https://github.com/llvm/llvm-project/pull/204088 : both the `widen add` and `widen sub`  intrinsics depend on the `widen` and `vector shift left and widen`  intrinsics. 

I would suggest that perhaps you could complete the `vector shift left and widen` intrinsics with the dependencies required for `widen add` in this single PR. Once both this PR and the other one  https://github.com/llvm/llvm-project/pull/204088  are merged, we can move forward, because the intrinsics not yet supported for `widen sub` also require `vector shift left and widen` support.

@banach-space  it's up to you to decide.

https://github.com/llvm/llvm-project/pull/204285