[clang] [clang][powerpc][wasm][systemz][x86] Replace target vector popcount intrinsics with __builtin_elementwise_popcount (PR #109160)

[Chen Zheng via cfe-commits]

chenzheng1030 wrote:

> Officially we don't guarantee target intrinsics at all - but I can add a release note if it will help?

hmm, I meant IBM OpenXLC compiler product doc, many builtins are listed there, not the community clang/llvm docs.

https://github.com/llvm/llvm-project/pull/109160