Improve compiler compatibility (#743)

* fix returns

* use standard C headers

* struct/class mismatch

* explicit this in template

* switch variable scope

* C standard compliance

* & l-value

include/JSystem/JAudio/JAIAnimation.h

@@ -3,7 +3,7 @@
 
 #include "dolphin/types.h"
 
-class Vec;
+struct Vec;
 class JAISound;
 class JAIBasic;
 namespace JAInter {

include/JSystem/JAudio/JASDrumSet.h

@@ -5,7 +5,7 @@
 
 namespace JASystem {
     class TInstEffect;
-    class TInstParam;
+    struct TInstParam;
 
     class TDrumSet : public TInst {
     public:

include/JSystem/JAudio/osdsp.h

@@ -3,6 +3,6 @@
 
 #include "dolphin/dsp.h"
 
-void DSPAddPriorTask(STRUCT_DSP_TASK*);
+void DSPAddPriorTask(DSPTaskInfo*);
 
 #endif /* OSDSP_H */

include/JSystem/JAudio/osdsp_task.h

@@ -8,7 +8,11 @@ typedef struct OSContext OSContext;
 
 extern DSPTaskInfo* DSP_prior_task;
 
+#ifdef __cplusplus
 extern "C" void __DSPHandler(int, OSContext*);
+#else
+void __DSPHandler(int, OSContext*);
+#endif
 void DsyncFrame2(u32, u32, u32);
 void Dsp_Update_Request();
 BOOL Dsp_Running_Check();