run cmake with -DANDROID_NDK_PATH=/path/to/ndk to generate the .aar & run the gradle build
if using Android Studio you will have to run the aar script manually(or do the cmake cmd) then put the normal cmake args inside '-PcmakeArgs="-DCMAKE_BUILD_TYPE=Release ...."' at `Settings > Build, Execution, Deployment > Gradle-Android Compiler > Command-line Options`
Check CMakeLists.txt Android build block for more info