Having a working cross toolchain is the starting point of a journey, not the end of it. At some point, you will want to begin cross compiling the various tools, applications, and libraries that you need on your target. Many of them will be open source packages, each of which has its own method of compiling, and each with its own peculiarities. There are some common build systems, including:
I will cover only the first two here since these are the ones needed for even a basic embedded Linux system. For CMake, there are some excellent resources on the CMake website referenced ...