[clang] [clang][CIR] Add lowering for Neon rounding builtins (PR #195021)

[Andrzej Warzyński via cfe-commits]

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

Thank you for the updates! I've left some comments inline. Also, could you delete the old tests that you used to create the new ones? We want to avoid test duplicaiton.

https://github.com/llvm/llvm-project/pull/195021