message: fix logic on windows avoiding copying of tbb.dll if already there
diff: @@ -44,19 +44,15 @@ endif
  $(LINK.cpp) $(subst \,/,$*.o) $(CMDSTAN_MAIN_O) $(LDLIBS) $(LIBSUNDIALS) $(MPI_TARGETS) $(TBB_TARGETS) $(subst \,/,$(OUTPUT_OPTION))
  ifeq ($(OS),Windows_NT)
  ifneq ($(notdir $(shell where tbb.dll)),tbb.dll)
  -ifneq ("$(wildcard $(@D)/tbb.dll)","")
  @echo 'Intel TBB is not in PATH.'
  @echo 'Consider calling '
  @echo 'make install-tbb'
  @echo 'to avoid copying Intel TBB library files.'
  - cp -v $(TBB_TARGETS) $(@D)
  -else
  - @echo 'Intel TBB is not in PATH, but found tbb.dll in model directory.'
  - @echo 'Using $(@D)/tbb.dll'
  - @echo 'Consider calling '
  - @echo 'make install-tbb'
  - @echo 'to ensure usage of correct Intel TBB version.'
  -endif
  + @if ! [[ -f "$(@D)/tbb.dll" ]]; then \
  + cp -v $(TBB_TARGETS) $(@D); \
  + else \
  + echo 'Using existing $(@D)/tbb.dll'; \
  + fi
  endif
  endif
  