- Constantine Sapuntzakis reported that Darwin 6.0 a.k.a. MAC OS X 10.2
and newer have a threadsafe getaddrinfo.
- Fix Dragonfly BSD triplet detection.
- In case the hard-coded knowledge says that getaddrinfo is threadsafe,
an additional check is done to verify that h_errno is also defined.
If h_errno isn't defined, we finally assume that it isn't threadsafe.
Jamie Lokier provided the inspiration for this extra check.
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