hdf5: link against MPI if a parallel HDF5 is found

See paraview/paraview#16814.

ThirdParty/hdf5/module.cmake

@@ -5,9 +5,20 @@ else()
 endif()
 if(VTK_USE_SYSTEM_HDF5)
   set(vtkhdf5_LIBRARIES ${HDF5_LIBRARIES} ${HDF5_HL_LIBRARIES})
+  if(NOT HDF5_IS_PARALLEL)
+    include(CheckSymbolExists)
+    set(CMAKE_REQUIRED_INCLUDES ${HDF5_INCLUDE_DIRS})
+    check_symbol_exists(H5_HAVE_PARALLEL hdf5.h HDF5_IS_PARALLEL)
+    unset(CMAKE_REQUIRED_INCLUDES)
+  endif()
+  if (HDF5_IS_PARALLEL)
+    include(vtkMPI)
+    list(APPEND vtkhdf5_LIBRARIES
+      ${MPI_C_LIBRARIES} ${MPI_CXX_LIBRARIES})
+  endif ()
 endif()
 vtk_module(vtkhdf5
   EXCLUDE_FROM_WRAPPING
   DEPENDS
     vtkzlib
-  )
\ No newline at end of file
+  )

ThirdParty/xdmf2/vtkxdmf2/CMakeLists.txt

@@ -38,23 +38,10 @@ if(EXISTS "${HDF5_CONFIG}")
   add_definitions(${HDF5_EXTRA_FLAGS})
 endif()
 
-# Some HDF5 configurations don't properly detect parallel support so
-# we need to do it manually ourselves
-if(NOT HDF5_IS_PARALLEL)
-  include(CheckSymbolExists)
-  set(CMAKE_REQUIRED_INCLUDES ${XDMF_HDF5_INCLUDE_DIRS})
-  check_symbol_exists(H5_HAVE_PARALLEL hdf5.h HDF5_IS_PARALLEL)
-  unset(CMAKE_REQUIRED_INCLUDES)
-endif()
-
 #optional dependencies
 #MPI
 option(XDMF_BUILD_MPI "XDMF should use MPI" OFF)
 mark_as_advanced(XDMF_BUILD_MPI)
-if(HDF5_IS_PARALLEL AND NOT XDMF_BUILD_MPI)
-  message(STATUS "Xdmf2: Enabling MPI since a parallel HDF5 is being used.")
-  set(XDMF_BUILD_MPI ON)
-endif()
 if (XDMF_BUILD_MPI)
   find_package(MPI REQUIRED)
   include_directories(${MPI_C_INCLUDE_PATH})