[libdispatch-dev] autoconf HAVE macro conventions

I'm not very familiar with autoconf conventions and was wondering why some config.h values are merely defined and some are explicitly defined to 1. Is there a strong convention to do #ifdef HAVE_FOO instead of #if HAVE_FOO when testing for configure features? For various reasons, the ability to define a macro to 0 or 1 would be useful for the Mac OS X version of config.h — it would let us define certain features in terms of other features without as much conditional logic. Kevin