This project showcases building three simple applications for the raspberry pi, cross-compiling them using cmake:

write-file prints a short message to the console and to a file. This is the simplest example, with no dependencies.
hello-asound prints the version of alsa on the system. The example demonstrates linking to a library installed on the system.
hello-portaudio tries to initialize portaudio. Another example of linking to a library, the difference this one is installed to /usr/lib.

Cross compilation has been tested on a linux machine as the host, and a Raspberry Pi 2 model B with Raspbian Stretch Lite as the target.

Howto:

Grab the compilers from https://github.com/raspberrypi/tools and put them somewhere on the host machine
Install the needed dependencies on the rpi: apt install libasound-dev libportaudio-dev
Mount the rpi filesystem locally on the host machine with sshfs (the cross-compilers will then be able to look for the dependencies in the mounted directory)
Provide the locations for the rpi-tools (see point 1) and the target sysroot (see point 3) to the rpi-toolchain.cmake script, by creating a toolchain-locations.cmake script with the definitions of the needed variables (see toolchain-locations-example.cmake for an example). Remember to never add toolchain-locations.cmake to version control.
Run cmake, providing the toolchain file, eg: mkdir build, then cd build and cmake ../ -DCMAKE_TOOLCHAIN_FILE=../rpi-toolchain.cmake
If the cmake step succeded, build the applications with make (you can also compile only one of the applications, eg: make write-file).
Copy the compiled executables to the mounted rpi filesystem, for example in the pi user home dir.
Open an ssh console session and launch the executable on the rpi.

Notes:

The setup/deployment process can be automated, and one nice way is using Qt-creator, which works well with cmake and can define kits for cross compilation and deployment to a remote device.
You can even build these examples on the rpi itself, you will of course need to install the dependencies but you won't otherwise need to provide a cmake toolchain file.