[clang] [CIR][AArch64] Upstream vmull_*/vmull_high_* Neon builtins (PR #188371)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space commented:

Thank you for working on this! Please see my comments inline.

https://github.com/llvm/llvm-project/pull/188371