Download waf (http://code.google.com/p/waf/)
autowaf.py is present in the tools directory of the Ardour source code.

From within the waf source tree, run:

./waf-light -v --make-waf --tools=misc,doxygen,/path/to/autowaf.py --prelude=''
cp ./waf /path/to/ardour/3.0/waf