Terminal doesn't start on old kernel

Commit 118ad1ca changes the VTE child setup function to prefer using the TIOCGPTPEER ioctl, and falls back to the old code if it isn't available (it was added in kernel 4.12). It checks for EINVAL to determine whether it should fall back. However, on a 3.10 armhf kernel (where I would expect it to fall back) I have observed that the error is actually ENOTTY. Because of this, the terminal never starts because the child process exits with 127 in its setup function.