Fix wrong forward declares (struct/class)

Requires removing the now-matching symbols from jsystem_stubs.cpp

include/Z2AudioLib/Z2LinkMgr.h

@@ -61,7 +61,7 @@ public:
     static Z2CreatureLink* getLink() { return mLinkPtr; }
 
     friend class Z2LinkSoundStarter;
-    friend class Z2RideSoundStarter;
+    friend struct Z2RideSoundStarter;
 
 private:
     /* 0x90 Z2LinkSoundStarter */

include/Z2AudioLib/Z2SoundObject.h

@@ -4,7 +4,7 @@
 #include "Z2AudioLib/Z2SoundHandles.h"
 #include "JSystem/JAudio2/JAUSoundAnimator.h"
 
-class Z2SoundStarter;
+struct Z2SoundStarter;
 
 class Z2SoundObjBase : public Z2SoundHandles
 #if DEBUG