If you come across this error while using cmake to build from source:
CMake Error: your CXX compiler: "CMAKE_CXX_COMPILER-NOTFOUND" was not found. Please set CMAKE_CXX_COMPILER to a valid compiler path or name.
It means that you don't have the build tools installed (the g++ in this case).
Open a terminal window and run:
sudo apt-get install build-essential -y