The Headerizer (tools/build/headerizer.pl) is a tool that generates chunks of .h header files based on C source code.
The long-term plan for the headerizer is that it will take all the prototypes for all the functions and populate all the .h files automatically. No need to worry about differences between header and source, because the header comes from it. It'll also auto-generate attributes for each of the functions that work with GCC.
Yesterday there was a problem where I forgot to put PARROT_EXPORT on the function in source, so linking on Windows broke. If that happens again, here's what you do:
The .h file should now have PARROT_EXPORT for the function in question.