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

include/JSystem/JStudio/JStudio/functionvalue.h

@@ -333,7 +333,11 @@ public:
             return r1.pf_ == r2.pf_;
         }
 
+#ifdef __MWERKS__
         f32 operator*() {
+#else
+        f32 operator*() const {
+#endif
             // this guard is required - removing it breaks float regalloc in std::upper_bound
             #if DEBUG
             JUT_ASSERT(947, pf_!=NULL);
@@ -444,7 +448,11 @@ public:
             return r1.pf_ == r2.pf_;
         }
 
+#ifdef __MWERKS__
         f32 operator*() {
+#else
+        f32 operator*() const {
+#endif
 #if DEBUG
             JUT_ASSERT(1098, pf_!=NULL);
 #endif