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

[Chen Zheng via cfe-commits]

chenzheng1030 wrote:

> @nemanjai Are you OK with the PPC changes?

on behalf of @nemanjai : ): the change LG to PPC.

FYI @lei137 @stefanp-ibm if we doc these builtins for PPC users, we may need to change the the docs.

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