To install unofficial Mapbox GL Native bindings for Qt QML from sources, you would have to install Qt version of MapboxGL native library. For that, please follow instructions at https://github.com/rinigus/pkg-mapbox-gl-native
After QMapboxGL is installed, proceed as follows.
Clone this repository
git clone https://github.com/rinigus/mapbox-gl-qml.git
Change to the directory, make build folder and start building:
cd mapbox-gl-qml
mkdir build && cd build
qmake ../mapbox-gl-qml.pro
make -j4
Install from build folder
sudo make install