[clang] [llvm] [HLSL] Implement elementwise popcount (PR #108121)

[Xiang Li via cfe-commits]

python3kgae wrote:

> This pull request is missing the appropriate text in 'ReleaseNotes.rst'. I am looking for advice on what is appropriate to put in that file, and where.

Here's a PR with ReleaseNotes.rst change https://github.com/llvm/llvm-project/commit/57f879cdd4c63189c569bdc1ce4e87e7342eea46#diff-ec770381d76c859f5f572db789175fe44410a72608f58ad5dbb14335ba56eb97

https://github.com/llvm/llvm-project/pull/108121