Define a dedicated `vmvar_t` type for values stored in variable pages
and propagate it through interfaces that expose those values. Keep the
type as int for now so this commit does not change runtime behavior.
This separates VM storage from ordinary int buffers and makes a later
conversion to 16-bit storage mechanically checkable.
We only support a fixed set of modules, so dynamic linking isn't really
necessary. This paves the way for running System3.9 games on more
platforms.
NIGHTDLL is temporarily disabled, because many symbols conflict with the
SACT module.
kichikuou