http://code.google.com/apis/v8/build.html
If you want to build v8 with GCC 4.x at x64 platform, you should compile v8 with PIC (Position-Independent Code) mode, and set the arch to x64 for scons.
export CCFLAGS=-fPIC
scons arch=x64
http://ant.apache.org/bindownload.cgi
$ export V8_HOME=<v8_path>
$ ant