CMake/Tests/ObjectLibrary/c.c

#if defined(_WIN32) && defined(Cshared_EXPORTS)
# define EXPORT_C __declspec(dllexport)
#else
# define EXPORT_C
#endif

extern int a1(void);
extern int a2(void);
extern int b1(void);
extern int b2(void);
EXPORT_C int c(void)
{
  return 0
    + a1()
    + a2()
    + b1()
    + b2()
    ;
}