sysinfo.h problem to compile

[Anton Gladky <gladky.anton@gmail.com>]

Hi, all

I have a very simple code:
=========
#include <sys/sysinfo.h>

int main() {
  struct sysinfo si;
}
=========

On KFreebsd it fails and causes FTBFS:
s.cpp:5:18: error: aggregate ‘main()::sysinfo si’ has incomplete type
and cannot be defined

On other systems it compiles without errors.
What can be a problem in?

Thanks
Anton