Block multiple inclusion because "Modules/CMakeCInformation.cmake"
includes "Platform/${CMAKE_SYSTEM_NAME}" even though the generic
module "CMakeSystemSpecificInformation.cmake" already included it.

The extra inclusion is a work-around to address issue #4772 without
intrusive platform file changes.  Once those changes are made the
work-around and these include blockers can be removed.  See issue #9656.