Windows build fixes

Name mangling/linkage shenanigans

Remove jsystem_stubs.cpp, it's not necessary.

include/JSystem/JAudio2/JASBank.h

@@ -4,7 +4,7 @@
 #include <dolphin/types.h>
 
 class JASChannel;
-class JASInstParam;
+struct JASInstParam;
 class JASWaveBank;
 
 namespace JASDsp {

include/JSystem/JAudio2/JASHeapCtrl.h

@@ -7,7 +7,7 @@
 #include <dolphin/os.h>
 #include <dolphin/os.h>
 
-class JASDisposer;
+struct JASDisposer;
 class JKRHeap;
 class JKRSolidHeap;
 

include/JSystem/JAudio2/JAUSectionHeap.h

@@ -14,8 +14,8 @@ class JASVoiceBank;
 class JAUBankTableLink;
 class JAUDisposer_;
 class JAUSectionHeap;
-class JAUSoundTable;
-class JAUSoundNameTable;
+struct JAUSoundTable;
+struct JAUSoundNameTable;
 class JKRArchive;
 class JKRSolidHeap;
 

include/c/c_damagereaction.h

@@ -21,7 +21,10 @@ extern u8 data_80450C9D;
 extern u8 data_80450C9E;
 extern u8 cDmr_FishingWether;
 extern u8 data_80450CA0;
-extern JPTraceParticleCallBack4 JPTracePCB4;
+
+extern "C" {
+    extern JPTraceParticleCallBack4 JPTracePCB4;
+}
 
 void debug_actor_create();
 

include/d/d_meter2_info.h

@@ -5,7 +5,7 @@
 
 class CPaneMgr;
 class J2DTextBox;
-struct JMSMesgEntry_c;
+class JMSMesgEntry_c;
 class JUTFont;
 
 struct dMenu_LetterData {