If file bav is missing from directory src/c/bav this means that compilation of C source code to executable file bav has not happened. This should happen in the last line of shell script make_backend.sh which is called in line 86 of the Ant script. Please check the output of the script for any error messages.
After I had installed libxml2-dev and libmilter-dev and set a simbolic link "conf" in /usr/share/tomcat6 to /etc/tomcat6 the build runs without an error.