[clang] [CIR][AArch64] Lower BF16 vduph lane builtins (PR #185852)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

@E00N777 Thanks for asking! That's exactly what I had in mind, yes. 

Btw, don't hesitate to ask if you get stuck. Also, it is totally expected that it takes a few iterations to get to the desirable implementation - that's part of the learning process!

https://github.com/llvm/llvm-project/pull/185852