Fix mergelibs build by adding dbtools to libmerged

Because svxcore links against dbtools since
86bdb137

Change-Id: Ibbdd76fc77c3739756d011ae0c1fd99bab57834b

solenv/gbuild/extensions/pre_MergedLibsList.mk

@@ -113,6 +113,7 @@ gb_MERGEDLIBS := \
 	canvastools \
 	configmgr \
 	cppcanvas \
+	$(call gb_Helper_optional,DBCONNECTIVITY,dbtools) \
 	deployment \
 	deploymentmisc \
 	$(if $(filter-out MACOSX WNT,$(OS)),desktopbe1) \