More to do, but this is a good start.

./build.sh release_gl -cc will cross compile setting the systemroot and gcc prefix to the following default values:

CCPREFIX=/home/pi/raspberrypi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-
CCSYSROOT=/home/pi/raspberrypi/sysroot

Edit them in ./build.sh to match your machine.