Fix 'fixme check'

The error produced by `make zipup` - but ignored by make - was:

```
...
fixme check
makefile_include.mk:448: recipe for target 'zipup' failed
make: [zipup] Error 123 (ignored)
mkdir -p libtomcrypt-...
```

makefile_include.mk

@@ -455,7 +455,7 @@ zipup: $(call print-help,zipup,Prepare the archives for a release) doc/crypt.pdf
 	@# files/dirs excluded from "git archive" are defined in .gitattributes
 	git archive --format=tar --prefix=libtomcrypt-$(VERSION)/ HEAD | tar x
 	@echo 'fixme check'
-	-@(find libtomcrypt-$(VERSION)/ -type f | xargs grep 'FIXM[E]') && echo '############## BEWARE: the "fixme" marker was found !!! ##############'
+	-@(find libtomcrypt-$(VERSION)/ -type f | xargs grep 'FIXM[E]') && echo '############## BEWARE: the "fixme" marker was found !!! ##############' || true
 	mkdir -p libtomcrypt-$(VERSION)/doc
 	cp doc/crypt.pdf libtomcrypt-$(VERSION)/doc/crypt.pdf
 	tar -c libtomcrypt-$(VERSION)/ | xz -6e -c - > crypt-$(VERSION).tar.xz