[libc-commits] [libc] [libc][stdbit] implement stdc_count_ones (C23) (PR #82444)

[Nick Desaulniers via libc-commits]

nickdesaulniers wrote:

Note to reviewers, this PR is stacked on top of #82440. Only https://github.com/llvm/llvm-project/pull/82444/commits/12feec53b8887f5509946ca8bdb28a5a99d79e1a and later should be reviewed in this PR.

https://github.com/llvm/llvm-project/pull/82444