message: Allow xattr -d to fail
diff: @@ -70,7 +70,7 @@ else ifneq ($(STANC_XATTR),)
  bin/stanc$(EXE) :
  cp bin/mac-stanc bin/stanc$(EXE)
  chmod +x bin/stanc
  - xattr -d com.apple.quarantine bin/stanc
  + -xattr -d com.apple.quarantine bin/stanc
  else ifneq (,$(wildcard bin/$(OS_TAG)-stanc))
  # use release stanc3 binary (Windows, Linux & MacOS releases before Catalina)
  