[llvm] [AMDGPU] Extend wave reduce intrinsics for i32 type (PR #126469)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> We need clang builtins and unit tests to ensure these really work

I could put some unit tests in `libc` if needed. I currently test the `scan` helpers in `gpuintrin.h` there.

https://github.com/llvm/llvm-project/pull/126469