how enable curl's AsynchDNS?

I want enable curl's AsynchDNS ( find in phpinfo() ) . What do i must do ? This is screenshot :

I found out install http://c-ares.haxx.se/

c-ares is a C library that performs DNS requests and name resolves asynchronously

http://curl.haxx.se/dev/readme-ares.ht开发者_JS百科ml But i still stuck at how install on curl exist.

libcurl needs to have been compiled and built for it. For Linux and other *nix systems, you can build with c-ares or the threaded-resolver to make it use asynchronous resolves.