Explicitly terminate some make rules

Generic rules like:

  %: %.in

have the downside that the source (%.in) itself matches the target
(via %.in: %.in.in). This leads to things like:

  Looking for a rule with intermediate file `doc/examples/hooks/ipsec.in.in'.
   Trying pattern rule with stem `ipsec.in.in'.
   Trying implicit prerequisite `doc/examples/hooks/ipsec.in.in.in'.
   Trying pattern rule with stem `ipsec.in.in'.
   Trying implicit prerequisite `doc/examples/hooks/ipsec.in.in.in'.
   Looking for a rule with intermediate file `doc/examples/hooks/ipsec.in.in.in'.
  Rejecting impossible implicit prerequisite `doc/examples/hooks/ipsec.in.in'.

To fix this, we need to tell make that such rules are terminating, so
that it doesn't recurse into them.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

Makefile.am

@@ -970,14 +970,14 @@ devel/upload: devel/upload.in $(REPLACE_VARS_SED)
 	sed -f $(REPLACE_VARS_SED) < $< > $@
 	chmod u+x $@
 
-daemons/%: daemons/%.in $(REPLACE_VARS_SED)
+daemons/%:: daemons/%.in $(REPLACE_VARS_SED)
 	sed -f $(REPLACE_VARS_SED) < $< > $@
 	chmod +x $@
 
-doc/examples/%: doc/examples/%.in $(REPLACE_VARS_SED)
+doc/examples/%:: doc/examples/%.in $(REPLACE_VARS_SED)
 	sed -f $(REPLACE_VARS_SED) < $< > $@
 
-doc/examples/hooks/%: doc/examples/hooks/%.in $(REPLACE_VARS_SED)
+doc/examples/hooks/%:: doc/examples/hooks/%.in $(REPLACE_VARS_SED)
 	sed -f $(REPLACE_VARS_SED) < $< > $@
 
 doc/examples/bash_completion: $(BUILD_BASH_COMPLETION) $(RUN_IN_TEMPDIR) \