Simplify and fix Avahi conditionals

Change-Id: Ied30c619804239044b935382d580dcb86bfb8b11

sd/CppunitTest_sd_uimpress.mk

@@ -71,28 +71,14 @@ $(eval $(call gb_CppunitTest_use_system_darwin_frameworks,sd_uimpress,\
 ))
 endif
 
-ifeq ($(OS), LINUX)
-ifeq ($(ENABLE_AVAHI),TRUE)
-$(eval $(call gb_Library_use_externals,sd,\
-    boost_headers \
-    gtk \
-    dbus \
-    avahi \
-))
-else
-$(eval $(call gb_Library_use_externals,sd,\
+$(eval $(call gb_CppunitTest_use_externals,sd_uimpress,\
     boost_headers \
     gtk \
     dbus \
+	$(if $(ENABLE_AVAHI), \
+	    avahi \
+	) \
 ))
-endif
-else
-$(eval $(call gb_CppunitTest_use_externals,sd_uimpress,\
-	boost_headers \
-        gtk \
-        dbus \
-))
-endif
 
 $(eval $(call gb_CppunitTest_add_exception_objects,sd_uimpress,\
     sd/qa/unit/uimpress \