Those are all consumed by our parser, so they all support comments.
I was considering whether they should have a license header at all,
but in the end I decided to add it because those files are often created
by copying parts of real unit files. And if the real ones have a license,
then those might as well. It's easier to add it than to make an exception.
Unfortunately meson does not install symlinks, but copies the symlink
destination instead. So symlinks need to be created by a script.
This commit adds both symlinks in test/testsuite-08.units/ and meson
scriptlet calls. Strictly speaking, the first is not necessary, since nothing
reads stuff directly from the source tree.
