Use AM_V_GEN in a few more places

Based on a patch by Javier Jardón in

https://bugzilla.gnome.org/show_bug.cgi?id=621720

Makefile.am

@@ -95,8 +95,7 @@ distclean-local:
 	fi
 
 ChangeLog:
-	@echo Creating $@
-	@if test -d "$(srcdir)/.git"; then \
+	$(AM_V_GEN) if test -d "$(srcdir)/.git"; then \
 	  (GIT_DIR=$(top_srcdir)/.git ./missing --run git log GTK_2_16_0^^.. --stat) | fmt --split-only > $@.tmp \
 	  && mv -f $@.tmp $@ \
 	  || ($(RM) $@.tmp; \