[clang] [CIR][AMDGPU] Add amdgcn wave reduce builtins codegen (PR #190137)

[Matt Arsenault via cfe-commits]

arsenm wrote:

Note there's https://github.com/llvm/llvm-project/pull/179589 which may change these quite a bit 

https://github.com/llvm/llvm-project/pull/190137