message: Remove existing stanc before copying built one
diff: @@ -51,7 +51,7 @@ ifneq ($(STANC3),)
  bin/stanc$(EXE) : $(call findfiles,$(STANC3)/src/,*.ml*) $(STANC#)
  @mkdir -p $(dir $@)
  cd $(STANC3) && echo "--- Rebuilding stanc ---\n" && dune build @install
  - cp $(STANC3)/_build/default/src/stanc/stanc.exe $@
  + test -f $(STANC3)/_build/default/src/stanc/stanc.exe && rm -f $@ && cp $(STANC3)/_build/default/src/stanc/stanc.exe $@ || exit 1
  else ifneq ($(STANC3_TEST_BIN_URL),)
  # download stanc3 build from specific branch
  ifeq ($(OS_TAG),windows)
  