Once more the people behind POSIX didn't think and put clock_gettime(2) and
friends in <time.h>. The kernel needs access to the associated #defines, but
can't get them from <time.h>, so introduce a new header <sys/_time.h> and
include that from <time.h> for userland and <sys/time.h> for the kernel.
ok matthew@, guenther@, millert@