[arch-general] Missing Dependency virtualbox-host-dkms

[Jack O'Connor]

> I didn't force the deps to linux-headers because you could use the kernel
> (linux, linux-lts, linux-zen, linux-grsec, etc) you prefer (or all together).
> I will add a message with the next release of virtualbox.

Would it be possible to depend on a "Provides" that all the different
kernel header packages share? Similar to how nvidia-libgl,
catalyst-libgl, and mesa-libgl all provide the "libgl" dependency.
That would solve the presumably-very-common case where users initially
installed virtualbox without any host headers at all, and are now
landing in a broken state by default. (Or would that mean that the
different header packages conflict where they didn't before?)

- Jack