illumos gate

And I quote:

int
custr_remove(custr_t *cus, size_t idx, size_t len)
{
        size_t endidx = idx + len;

        /*
         * Once gcc4 is dropped as a shadow compiler, we can migrate to
         * using builtins for the overflow check.
         */
        if (endidx < idx || endidx < len) {
                errno = EINVAL;
                return (-1);
        }

Now that gcc4 is officially gone, this comment can be acted upon.