Set preferred dns servers
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_SERVERS, char *servers);
Pass a char * that is the list of DNS servers to be used instead of the system default. The format of the dns servers option is:
NULL - use system default
This option requires that libcurl was built with a resolver backend that supports this operation. The c-ares backend is the only such one.
Added in 7.24.0
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, CURLE_NOT_BUILT_IN if support was disabled at compile-time, CURLE_BAD_FUNCTION_ARGUMENT when given an invalid server list, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.