[llvm] [clang] [AMDGPU] Improve selection of ballot.i64 intrinsic in wave32 mode. (PR #71556)

[Valery Pykhtin via cfe-commits]

vpykhtin wrote:

I'm going to rebase it on top of https://github.com/llvm/llvm-project/pull/73779 to show test changes.

https://github.com/llvm/llvm-project/pull/71556