[C++] Use software __builtin_popcountll when building without SSE4.2

[asfimport]

This is to be extra safe in the context of ARROW-5381

Reporter: Wes McKinney / @wesm

Related issues:

• [C++] Crash at arrow::internal::CountSetBits (is a child of)
• [C++] signal SIGILL raised by Illegal instruction

_{Note: This issue was originally created as ARROW-6663. Please see the migration documentation for further details.}

[rvschaffer]

Hi @asfimport , I'm on old hardware enthusiast (haha), and this issue is really a showstopper for me! There are many other in the same situation. Please make Arrow usable on "popcnt'less" CPUs, so we can continue using them.

[abcbarryn]

I see this still hasn't been fixed. Is Pyarrow no longer maintained?

[github-actions[bot]]

This issue has been marked as stale because it has had no activity in the past 365 days. Please remove the stale label or comment below, or this issue will be closed in 14 days. If this improvement is still desired but has no current owner, please add the 'Status: needs champion' label.

[abcbarryn]

How do I add "Status: needs champion"???

[abcbarryn]

Wow, over 3900+ open issues, 356 with stale/inactivity warnings, and this one with no assignee or response for a year?!? It looks like PyArrow is now unmaintained. Time to look for alternatives. :(