to be specified as a dependency of packages that require `lib/libGL.so`
and friends.
Currently `lib/libGL.so` is provided by `libglvnd` package. Depending on
`libglvnd`, however, would not work, because `libglvnd` does not depend
on any provider of OpenGL implementation (`mesa` is a recommendation.)
At least one provider should be hard-depended on, not only recommended.