Resolve compile warnings in modern

src/pokemon_storage_system.c

@@ -464,6 +464,9 @@ EWRAM_DATA static u8 sMovingMonOrigBoxPos = 0;
 EWRAM_DATA static bool8 sCanOnlyMove = 0;
 
 // This file's functions.
+#if !defined(NONMATCHING) && MODERN
+#define static
+#endif
 static void CreatePCMenu(u8 whichMenu, s16 *windowIdPtr);
 static void Cb2_EnterPSS(u8 boxOption);
 static u8 GetCurrentBoxOption(void);