fix gcc 4.2 warnings about cast from pointer to integer (#3317)

code/game/g_local.h

@@ -712,7 +712,7 @@ void BotTestAAS(vec3_t origin);
 extern	level_locals_t	level;
 extern	gentity_t		g_entities[MAX_GENTITIES];
 
-#define	FOFS(x) ((int)&(((gentity_t *)0)->x))
+#define	FOFS(x) ((size_t)&(((gentity_t *)0)->x))
 
 extern	vmCvar_t	g_gametype;
 extern	vmCvar_t	g_dedicated;