Why some of the apache server functions are declared with APU_DECLARE()? -

i source code of apache server, of function declared below:

apu_declare(const char *) apr_xml_empty_elem(apr_pool_t *p,const apr_xml_elem *elem); 

apu_declare definition declared follow:

#define apu_declare(type)   type 

i not understand why this. apu_declare seems useless. have special meaning?

it's #define apu_declare(type) __declspec(dllimport) type __stdcall win32.

it allows them cross platform.