BUG #5394: invalid __declspec for PG_MODULE_MAGIC

The following bug has been logged online:

Bug reference:      5394
Logged by:          Vladimir Barzionov
Email address:      snego.barsik@gmail.com
PostgreSQL version: 8.3.10
Operating system:   win32
Description:        invalid __declspec for PG_MODULE_MAGIC
Details:

In fmgr.h,
macros PG_MODULE_MAGIC, PG_FUNCTION_INFO_V1.. are declared with incorrect
"storage-class". It uses PGDLLIMPORT for declare __declspec().

In general for building external DLL module, PGDLLIMPORT must be
__declspec(dllimport). As it is.

However in PG_MAGIC_* macro, storage class for function must be
__declspec(dllexport).

Same problem was already discussed for example here
http://dbaspot.com/forums/postgresql/393683-re-general-custom-c-function-pal
loc-broken.html

Looks like the simplest way for correcting the issue is declaring additional
macro (something like PGMODULEEXPORT)