Freetype and Harfbuzz have a cyclic dependency which makes it a bit more work when you want to use these libraries as an External Project with CMake.
This repository contains an example on how you can build Freetype and HarfBuzz with support for each other. First we compile Freetype without HarfBuzz support, then we compile HarfBuzz with Freetype support and then we recompile Freetype again with HarfBuzz support.
I've tested this on Arch Linux, GCC 9.2.1 and on Windows 10 with Visual Studio Community 2019.
git clone git@github.com:roxlu/cmake-freetype-harfbuzz.git
cd cmake-freetype-harfbuzz
./build.sh
Open a "x64 Native Tools Command Prompt for VS 2019" and execute:
git clone git@github.com:roxlu/cmake-freetype-harfbuzz.git
cd cmake-freetype-harfbuzz
./build.bat