Make some global variables less-global (static)

Make some global variables less-global (static)

Explicitly make these global variables less-global to reduce the maximum
scope of this global state.

In my experience global variables tend to be a major source of bugs. As
such the less accessible they are the less likely they are to be the
source of a bug.

Signed-off-by: Giel van Schijndel <me@mortis.eu>