os_version, os_revision - Version of the OS currently running. Allegro game
extern int os_version;
extern int os_revision;
The major and minor version of the Operating System currently running. Set by
allegro_init(). If Allegro for some reason was not able to retrieve the
version of the Operating System, os_version and os_revision will be set to -1.
For example: Under Win98 SE (v4.10.2222) os_version will be set to 4 and
os_revision to 10.