Re: Add PGDLLEXPORT to PG_FUNCTION_INFO_V1

I wrote:
> No, it's cross *file* references within a single contrib module that
> would be likely to need extern declarations in a header file.  That's
> not especially weird IMO.  I'm not sure how many cases there actually
> are though.

I poked at this a little bit.  AFAICT, the only actual cross-file
references are in contrib/ltree/, which has quite a few.  Maybe we
could hold our noses and attach PGDLLEXPORT to the declarations in
ltree.h.

hstore's HSTORE_POLLUTE macro would also need PGDLLEXPORT-ification,
but that's just within the macro so it wouldn't be too ugly.

The other problem is xml2's xml_is_well_formed(), which duplicates
the name of a core backend function.  If we PGDLLEXPORT-ify that,
we get conflicts against the core's declaration in utils/xml.h.
I do not see any nice way to dodge that.  Maybe we could decide that
six releases' worth of backwards compatibility is enough and
just drop it from xml2 --- AFAICS, that would only break applications
that had never updated to the extension-ified version of xml2 at all.
        regards, tom lane