Resolve externed prototypes in C files

include/overworld.h

@@ -143,5 +143,7 @@ bool32 sub_8058318(void);
 void CB2_ReturnToStartMenu(void);
 void CB2_WhiteOut(void);
 void c2_8056854(void);
+void sub_8054F38(u32 newKey);
+void sub_8055778(int);
 
 #endif //GUARD_OVERWORLD_H