Since this tool has many dependenciess it's a good idea to build in a docker container. Luckily the tool provides some Dockerfiles which simplifies tracking down said dependencies.
First get the repo. This will take you to master, if you want to play it safe you can checkout a tagged release.
git clone https://github.com/crosstool-ng/crosstool-ng.git
Then build the container. If the distro version you're rocking is not available, choose an older version or create your own Dockerfile. I'll use the 18.04 Dockerfile for my Ubuntu 20.04 PC.