Newest FindMPI incompatible with cmake < 3.18
The FindMPI patch in !8322 (merged) causes config errors with cmake 3.16 when
VTK_USE_MPI is enabled:
CMake error at CMakeFiles/CMakeTmp/CMakeLists.txt:20 (target_link_libraries): Error evaluating generator expression: $<HOST_LINK:SHELL:-pthread> Expression did not evaluate to a known generator expression CMake Error at CMake/patches/3.22/FindMPI.cmake:1266 (try_compile): Failed to generate test project build system. Call Stack (most recent call first): CMake/patches/3.22/FindMPI.cmake:1317 (_MPI_try_staged_settings) CMake/patches/3.22/FindMPI.cmake:1607 (_MPI_check_lang_works) CMake/vtkModule.cmake:4360 (find_package) CMake/vtkModule.cmake:4960 (vtk_module_find_package) Utilities/MPI/CMakeLists.txt:1 (vtk_module_third_party_external)
Currently, VTK is targeting compatibility with cmake 3.12 and above.