Resolve compile warnings in modern

src/battle_main.c

@@ -72,6 +72,9 @@ extern const u8 *const gBattlescriptsForUsingItem[];
 extern const u8 *const gBattlescriptsForSafariActions[];
 
 // this file's functions
+#if !defined(NONMATCHING) && MODERN
+#define static
+#endif
 static void CB2_InitBattleInternal(void);
 static void CB2_PreInitMultiBattle(void);
 static void CB2_PreInitIngamePlayerPartnerBattle(void);