message: BUGFIX: add missing option to use 64-bit indices
diff: option(AXOM_ENABLE_SPARSEHASH "Enables Sparsehash." ON)
  option(AXOM_ENABLE_ALL_COMPONENTS "Enables all components by default" ON)
  +option(AXOM_USE_64BIT_INDEXTYPE "Use 64-bit integers for axom::IndexType" OFF)
  if(NOT CMAKE_CONFIGURATION_TYPES)
  if(CMAKE_BUILD_TYPE MATCHES "(Debug|RelWithDebInfo)")
  