message: Adds some comments, per PR suggestions
diff: @@ -33,11 +33,11 @@ elseif("${_axom_debug_define_upper}" MATCHES "OFF|FALSE")
  # no-op
  elseif("${_axom_debug_define_upper}" MATCHES "DEFAULT")
  # Default behavior is to be on for Debug and RelWithDebInfo configurations and off otherwise
  - if(NOT CMAKE_CONFIGURATION_TYPES)
  + if(NOT CMAKE_CONFIGURATION_TYPES) # This case handles single-config generators, e.g. make
  if( CMAKE_BUILD_TYPE MATCHES "(Debug|RelWithDebInfo)" )
  set(AXOM_DEBUG_DEFINE_STRING "AXOM_DEBUG")
  endif()
  - else ()
  + else () # This case handles multi-config generators, e.g. MSVC
  set(AXOM_DEBUG_DEFINE_STRING "$<$<CONFIG:Debug,RelWithDebInfo>:AXOM_DEBUG>")
  endif()
  else() # Handle bad value for AXOM_DEBUG_DEFINE config variable
  