When DKMS uses `clang` to compile the `nvidia` kernel driver, you're boned.

```bash
sudo modprobe nvidia
modprobe: ERROR: could not insert 'nvidia': Exec format error
```

Unfortunately, `dkms` doesn't take `CC` and `CXX` settings from the environment.

```bash
sudo update-alternatives --config cc
sudo update-alternatives --config c++
sudo dkms remove nvidia/390.48 -k 4.15.0-32-generic
sudo dkms build nvidia/390.48 -k 4.15.0-32-generic
sudo dkms install nvidia/390.48
sudo modprobe nvidia
```

And reboot.