Should compiler generate an error at the time of compiler?

["Sergey M. Samoylov" <ssamoylov@xxxxxxxxxxxxx>]

I have a code with mistake:

extern int errno;
main()
{
	printf("errno=%d",errno);
}
Why in any cross gcc compilers when it compiler, compiler will pass?
Why compiler will not say me about any mistakes like:
: undefined reference to 'errno'

It's just only in cross compiler in usuall compiler gcc-3.3.1 it's OK and 
compiler generate the error.
Best Regards
Sergey Samoylov