2.83.7
fix whitespace formatting in cmake files
remove unused function in btRigidBody (btSetCrossMatrixMinus) thanks to Stefan for reporting.
ftello64 -> ftell and fopen64 -> fopen (to make Mac OSX happy) disable some warning (no idea why weak_link is there)
fix cmake to succeed with -DBUILD_BULLET3=0
fix and re-enable sphere-box collision algorithm, Issue 643
add a btFixedConstraint with toggle between btGeneric6DofConsraint and btFixedConstraint in VoronoiFractureDemo