should install autotools.
sudo apt-get install build-essential
FYI, I think that the memcached module will only work when is compiled along with Varnish - meaning that you will have to compile Varnish as well.
Personally, I think that Varnish is already top of the performance without adding anything extra. Most of the other things will have to do with how the page actually loads things (See Google Pagespeed for Apache, and Google Pagespeed for Nginx which is in my signature), and technologies such as SPDY (for SSL). Compressing the page and/or using a CDN to reach places that your server is far from also helps.
A setup like Varnish -> Nginx -> php5-fpm (xcache) is already quite fast if Varnish is tuned properly (i.e. stripping cookies where appropriate to allow Varnish to cache things) as Varnish serves from memory