When looping in this function and checking for the timeout being
expired, it was not updating the reference time when calculating the
timediff since previous round which made it think each subsequent loop
to have taken longer than it actually did.

I also modified the function to use the generic Curl_timeleft() function
instead of the custom logic.

Bug: http://curl.haxx.se/bug/view.cgi?id=3112579

When send() and recv() fail, we now store the errno value to allow the
app to access it.

Bug: http://curl.haxx.se/bug/view.cgi?id=3128121
Reported by: Yuri

- Show address string from proper buffer in case of connection failure.

- Try next address when inet_ntop() fails.

and the traditional source header

Reinstate IPV6 build variable that got removed.

Failed to commit this file changes along with the others.

warning C4146: unary minus operator applied to unsigned type, result still unsigned

Ensure that spurious results from system's getaddrinfo() ares not propagated
by Curl_getaddrinfo_ex() into the library.

Also ensure that the ai_addrlen member of Curl_getaddrinfo_ex()'s output linked
list of Curl_addrinfo structures has appropriate family-specific address size.

... not the proxy port.  It makes no difference unless a proxy is used.

Winsock builds clobber some errno.h defines in setup_once.

This showed a problem when running the test out-of-tree, so
an include path is now being added to pick up the generated
curlbuild.h file.