[Bug c/100671] override-init suppressed in 'two shot' compilation when initializer macro/value is defined in system header file

[jan.smets at nokia dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100671

--- Comment #1 from Jan Smets <jan.smets at nokia dot com> ---
Another one we've had problems with is quite similar. The example below is a
void function trying to return a value. 

#if 1
  /* NULL defined in a system header file
    => warning in "one shot" compilation.
    => no warning in "two shot" compilation. */
  #include <stddef.h>
#else
  /* always warns */
  #define NULL (0L)
#endif

void test(void)
{
    return NULL;
}