We require a similar change to https://github.com/bitcoin/bitcoin/pull/15939/files#diff-ff7aa83852bca28e4ff420bc97c6cf7c in contrib/teamcity/setup-debian-buster.sh You happened to catch me mid-migration, so you wouldn't see test failures for this quite yet. If you'd prefer to coordinate on this in separate diff, let me know.
Also, summarizing a discussion I had with Fabien offline:
I'm of the opinion that cleaning up our codebase to get rid of 32-bit-supporting features (like reverting D5587 for example) would put us in a better state. It improves code readability to simply not have these sorts of changes when they aren't needed. Currently, our assumptions are that C++11 is well supported. Reverting D5587 would also be in line with the same spirit as D2219, which had a similar removal. However, cleaning this up too aggressively has two factors that oppose this: merge conflicts when backporting, and sudden breakage of support for 32-bit Windows. While the release containing this change will no longer support 32-bit, it seems prudent to not immediately break it while these users (if any) transition.
Fabien prefers to go through a transition period where we do not deliberately break 32-bits to our knowledge. Personally, I don't agree but do not feel the upsides to be strictly strong enough to block this change.