Cleanly shut down JKRDecomp thread

Properly join the thread to ensure it's shut down before we try to exit.

Fixes #268

libs/JSystem/include/JSystem/JFramework/JFWSystem.h

@@ -33,6 +33,9 @@ struct JFWSystem {
 
     static void firstInit();
     static void init();
+#if TARGET_PC
+    static void shutdown();
+#endif
 
     static JUTConsole* getSystemConsole() { return systemConsole; }
     static JKRExpHeap* getSystemHeap() { return systemHeap; }

libs/JSystem/include/JSystem/JKernel/JKRAram.h

@@ -39,6 +39,9 @@ public:
 
 public:
     static JKRAram* create(u32, u32, s32, s32, s32);
+#if TARGET_PC
+    static void destroy();
+#endif
     static void checkOkAddress(u8*, u32, JKRAramBlock*, u32);
     static void changeGroupIdIfNeed(u8*, int);
     static JKRAramBlock* mainRamToAram(u8*, u32, u32, JKRExpandSwitch, u32, JKRHeap*, int, u32*);

libs/JSystem/include/JSystem/JKernel/JKRDecomp.h

@@ -48,6 +48,9 @@ private:
 
 public:
     static JKRDecomp* create(s32);
+#if TARGET_PC
+    static void destroy();
+#endif
     static JKRDecompCommand* prepareCommand(u8*, u8*, u32, u32, JKRDecompCommand::AsyncCallback);
     static void sendCommand(JKRDecompCommand*);
     static bool sync(JKRDecompCommand*, int);