Fix MSVC compiler and linker errors

- Fix struct/class forward declaration mismatches (JAIAudience, JASTrack) causing different MSVC mangled names and unresolved symbols
- Add jsystem_stubs.cpp with stubs for JASHeap, JASVoiceBank, J3DShapeTable, JAUSection, JHICommBuf, HIO/HIO2, JOR

src/dusk/extras.cpp

@@ -1,6 +1,9 @@
 // C++ Mangled version of extras.c
 #include <cstring>
 #include <cstdint>
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
 
 void *__memcpy(void* dest, void const* src, int n) {
     return memcpy(dest, src, n);
@@ -14,5 +17,11 @@ void __dcbz(void* addr, int offset) {
 
 int __cntlzw(unsigned int val) {
     if (val == 0) return 32; // PowerPC returns 32 if the input is 0
+#ifdef _MSC_VER
+    unsigned long idx;
+    _BitScanReverse(&idx, val);
+    return 31 - (int)idx;
+#else
     return __builtin_clz(val);
+#endif
 }