Merge topic 'fix_mpi_build_issues'

5b2d8b8e Fix incorrect error when testing is disabled.

Acked-by: Kitware Robot <kwrobot@kitware.com>
Reviewed-by: David E DeMarle <dave.demarle@kitware.com>
Merge-request: !510

CMake/vtkTestingMPISupport.cmake

@@ -28,7 +28,10 @@ if(MPIEXEC)
   set(VTK_MPI_MAX_NUMPROCS ${MPIEXEC_MAX_NUMPROCS} CACHE STRING
     "Maximum number of processors available to run parallel applications. (see ${CMAKE_CURRENT_SOURCE_DIR}/CMakeLists.txt for more info.)" FORCE)
 else()
-  message(FATAL_ERROR "MPIEXEC was empty.")
+  if(BUILD_TESTING)
+    # This is not a fatal error unless testing is enabled.
+    message(FATAL_ERROR "MPIEXEC was empty.")
+  endif()
 endif()
 
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