Note the -H (source directory) and -B (build directory) have always been undocumented, internal arguments to cmake (SO). This changed in CMake 3.13 (ref1, ref2) in such a manner that -S (not -H) and -B are now officially documented, but the old -H changed its meaning to a new alias for --help.
Spawned from https://github.com/roboticslab-uc3m/kinematics-dynamics/issues/187#issuecomment-648767401: