Look like it is working as expected.
- Install CMake 3.11
- Install ninja with job server support
- Configure using:
~/Software/cmake-3.11.0-Linux-x86_64/bin/cmake \
-GNinja \
-DQt5_DIR:PATH=$Qt5_DIR \
-DCMAKE_BUILD_TYPE:STRING=Release \
'-DCMAKE_JOB_POOLS:STRING=compile=4;link=3' \
-DCMAKE_JOB_POOL_COMPILE:STRING=compile \
-DCMAKE_JOB_POOL_LINK:STRING=link \
../Slicer-Qt5-VTK9
Make sure you add the extra quote around -DCMAKE_JOB_POOLS:STRING=compile=4;link=3