easy: Fix curl_easy_duphandle for builds missing IPv6 that use c-ares

easy: Fix curl_easy_duphandle for builds missing IPv6 that use c-ares

- Ignore CURLE_NOT_BUILT_IN errors returned by c-ares functions in
  curl_easy_duphandle.

Prior to this change if c-ares was used as the resolver backend and
either it was too old or libcurl was built without IPv6 support then
some of our resolver functions could return CURLE_NOT_BUILT_IN to
curl_easy_duphandle causing it to fail.

Caused by c8f086b which shipped in 7.69.1.

Reported-by: Karl Chen
Fixes https://github.com/curl/curl/issues/5097
Closes https://github.com/curl/curl/pull/5100