message: ensure that tbb.dll only gets copied once per directory
diff: # Build test executables
  ##
  +LIB_DIRS_FULL=$(filter %/, $(wildcard src/test/interface/*/) src/test/interface/)
  +LIB_DIRS_TBB=$(LIB_DIRS_FULL:src/%/=%/tbb-lib)
  +LIB_DIRS_TBB_TARGETS=$(foreach subdir, $(LIB_DIRS_TBB), tests-tbb-install/$(subdir))
  +
  +tests-tbb-install/% :
  + @mkdir -p $(dir $*)
  +ifeq ($(OS),Windows_NT)
  + cp -v $(TBB_TARGETS) $(dir $*)
  +endif
  + @touch $*
  +
  test/%$(EXE) : CXXFLAGS += $(CXXFLAGS_GTEST)
  test/%$(EXE) : CPPFLAGS += $(CPPFLAGS_GTEST)
  test/%$(EXE) : INC += $(INC_GTEST) -I $(RAPIDJSON)
  -test/%$(EXE) : test/%.o $(GTEST)/src/gtest_main.cc $(GTEST)/src/gtest-all.o $(LIBSUNDIALS) $(MPI_TARGETS) $(TBB_TARGETS)
  - $(LINK.cpp) $(filter-out src/test/test-models/% src/%.csv bin/% test/%.hpp %.hpp-test,$^) $(LDLIBS) $(OUTPUT_OPTION)
  -ifeq ($(OS),Windows_NT)
  -ifneq ($(notdir $(shell where tbb.dll)),tbb.dll)
  - @echo 'Intel TBB is not in PATH. Consider calling '
  - @echo 'make install-tbb'
  - @echo 'to avoid copying Intel TBB library files.'
  - cp -v $(TBB_TARGETS) $(@D)
  -endif
  -endif
  +test/%$(EXE) : test/%.o $(GTEST)/src/gtest_main.cc $(GTEST)/src/gtest-all.o $(LIBSUNDIALS) $(MPI_TARGETS) $(TBB_TARGETS) $(LIB_DIRS_TBB_TARGETS)
  + $(LINK.cpp) $(filter-out src/test/test-models/% src/%.csv bin/% test/%.hpp %.hpp-test %/tbb-lib,$^) $(LDLIBS) $(OUTPUT_OPTION)
  test/%.o : src/test/%.cpp
  @mkdir -p $(dir $@)
  