Incorrect set command in vtkCompilerPlatformFlags.cmake
On line 125 of CMake/vtkCompilerPlatformFlags.cmake you'll find:
set(CMAKE_CXX_MP_NUM_PROCESSORS CACHE ${PROCESSOR_COUNT} "The maximum number of processes for the /MP flag")
This isn't right and throws a warning. The line should be:
set(CMAKE_CXX_MP_NUM_PROCESSORS ${PROCESSOR_COUNT} CACHE STRING "The maximum number of processes for the /MP flag")
This is according to the documentation for the CMake set command https://cmake.org/cmake/help/v3.14/command/set.html