[Hampshire] gcc - disabling builtin macros?

Hi All.

I'm trying to get gcc to do some preprocessing - but I really don't want
its built-in macros (I'm trying to derive some stuff from another
toolchain's header files, and gcc is the best tool I've got for this).

Does anyone know how to disable the builtin macros? I've tried
"-fno-builtin", but it still uses them :-(

Thanks!

Vic.