Add the compile-time SDL major version option and propagate it through
interface targets. Route SDL includes through C99 compatibility headers
while keeping SDL2 as the desktop and Emscripten default.
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.
Instead of hardcoding "dDEMO.alk" / "tDEMO.alk", use the actual filename
stored in nact->files.alk[0] from the directory scan. This fixes loading
failures on case-sensitive filesystems where the actual file may be
named "dDemo.alk" or "tDemo.alk".
Also update gameresource.c to store .alk files without a numeric suffix
at index 0 (these games have only one .alk file).
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