GNU Make also has a few simple features that are very convenient. Forexample, the -o file option which says ``pretend thatsource file file has not changed, even though it has changed.''This is extremely useful when you add a new macro to a header file.Most versions of Make will assume they must therefore recompile all thesource files that use the header file; but GNU Make gives you a way toavoid the recompilation, in the case where you know your change to theheader file does not require it.