x64: Workaround for MSVC build issue.

src/lj_err.c

@@ -378,7 +378,7 @@ typedef struct UndocumentedDispatcherContext {
   ULONG64 EstablisherFrame;
   ULONG64 TargetIp;
   PCONTEXT ContextRecord;
-  PEXCEPTION_ROUTINE LanguageHandler;
+  void (*LanguageHandler)(void);
   PVOID HandlerData;
   PUNWIND_HISTORY_TABLE HistoryTable;
   ULONG ScopeIndex;