message: Use actual break in unistd/brk
diff: #include "test_helpers.h"
  int main(void) {
  - int status = brk((void*)100);
  + void * current = sbrk(0);
  + ERROR_IF(sbrk, current, == (void *)-1);
  +
  + int status = brk(current + 4096);
  ERROR_IF(brk, status, == -1);
  UNEXP_IF(brk, status, != 0);
  }
  