knowledge says the contrary or h_errno is not defined.

- 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.

Add some comments to better understand what the regex's pretend to achieve.

Refactor how libraries are checked for connect() function,
and check for connect() as it is done for other functions.

check for socket() and closesocket() as it is done for other functions

HAVE_IOCTL_SIOCGIFADDR since it's needed to use SIOCGIFADDR and Watcom C
doesn't currently define it.

used, and define HAVE_IOCTL_SIOCGIFADDR if appropriate.

checks for inet_ntoa_r() inet_ntop() and inet_pton()

non-blocking mode, and decouple function detection from function capability.

 and CHECK_FUNC_GETADDRINFO_UNFREEABLE_AI_CANONNAME
internal to CHECK_FUNC_GETADDRINFO

function returns an addrinfo with an unfreeable ai_canonname member ptr.

function returns an addrinfo with an unfreeable ai_addr member ptr.

inet_pton function is available.

inet_ntop function is available.

check for winsock build target configurations

that lacks the writev function.

  strcasecmp()
  strcmpi()
  stricmp()
  strncasecmp()
  strncmpi()
  strnicmp()