it downloads, extracts and prepares linux source using toolchain64 cross compiler
./module-prepare.sh
after that you should be able to compile modules by running
export PATH=/usr/local/x64/bin:$PATH
make -C /path/to/linux M=$PWD ARCH=x86_64 CROSS_COMPILE=x86_64-unknown-linux-gnu- modules
use strip of cross compiler for stripping unneccessary debugging symbols
find -type f -name "*.ko" -exec x86_64-unknown-linux-gnu-strip --strip-unneeded {} \;
also you can compress modules
find -type f -name "*.ko" -exec gzip {} \;