cares: sync with upstream, fully adopt v1.12.0
Not a big change but previous sync's have been piecemeal so this is a full job. I've also redone most of the config headers in config/ (haven't touched the AIX one but it still compiles and passes).
Passing CI @ https://ci.nodejs.org/job/node-test-commit/5830/ minus unrelated freebsd failures.
I believe this is ABI and API stable so could be backported through to v4.x.