##  This rule doesn't work for BSD-style make, but it's fine for
##  GNU make.
.%.o.d: %.cc
	@echo building dependencies for $<
	@$(CXX) -MM $(CXXFLAGS) $< > $@.$$$$; \
           sed 's,\($*\)\.o[ :]*,\1.o $@ : ,g' < $@.$$$$ > $@; \
           rm -f $@.$$$$