message: Fix
  I finally went and read about C++ linking and understand why link
  order matters and how to use it. This helped me a great deal:
diff: @@ -38,7 +38,7 @@ endif
  @echo ''
  @echo '--- Compiling, linking C++ code ---'
  $(COMPILE.cpp) $(CXXFLAGS_PROGRAM) -x c++ -o $*.o $<
  - $(LINK.cpp) $(LDLIBS) $(CMDSTAN_MAIN_O) $(LIBSUNDIALS) $(MPI_TARGETS) $*.o $(OUTPUT_OPTION)
  + $(LINK.cpp) $*.o $(CMDSTAN_MAIN_O) $(LDLIBS) $(LIBSUNDIALS) $(MPI_TARGETS) $(OUTPUT_OPTION)
  ##
  