LWG2727: Parallel algorithms with constexpr specifier

[cjdb]

Link: https://wg21.link/lwg2727

[llvmbot]

@llvm/issue-subscribers-c-17

Author: Christopher Di Bella (cjdb)

[frederick-vs-ja]

LWG3303 (see also #101693) is also in this area.

Both LWG issues seem "Nothing to do" as they're just saying not to add constexpr, and we haven't added anything because the parallel versions are not yet implemented.
However, it also possibly makes sense to consider either issue "Complete" when the corresponding parallel algorithms are implemented.

[mordante]

I dislike closing these as Nothing To Do/Complete. When somebody implements the paper that introduces these constexpr changes they might get reviewed and accepted as constexpr. I've seen bugs in libc++ due to closing issues "too early". I much rather close them with the PR that implements the paper.