Fix date command invocation on OS X (#34172)

BSD derived `date` doesn't like having the format option before
other options to `date`. Reverse the order appropriately.

Author: Keno

Makefile

@@ -583,7 +583,7 @@ testall1: check-whitespace $(JULIA_BUILD_MODE)
 	@env JULIA_CPU_THREADS=1 $(MAKE) $(QUIET_MAKE) -C $(BUILDROOT)/test all JULIA_BUILD_MODE=$(JULIA_BUILD_MODE)
 
 test-%: check-whitespace $(JULIA_BUILD_MODE)
-	@([ $$(( $$(date +%s) - $$(date +%s -r $(build_private_libdir)/sys.$(SHLIB_EXT)) )) -le 100 ] && \
+	@([ $$(( $$(date +%s) - $$(date -r $(build_private_libdir)/sys.$(SHLIB_EXT) +%s) )) -le 100 ] && \
 		printf '\033[93m    HINT The system image was recently rebuilt. Are you aware of the test-revise-* targets? See CONTRIBUTING.md. \033[0m\n') || true
 	@$(MAKE) $(QUIET_MAKE) -C $(BUILDROOT)/test $* JULIA_BUILD_MODE=$(JULIA_BUILD_MODE)