Support demand paging via closures and seh

Reverts 12a79192ee which exploits normal tcg mechanism

This uses a trampoline to pass extra data to seh handlers

include/uc_priv.h

@@ -399,6 +399,11 @@ struct uc_struct {
     struct TranslationBlock *last_tb; // The real last tb we executed.
 
     FlatView *empty_view; // Static function variable moved from flatviews_init
+
+#ifdef WIN32
+    PVOID seh_handle;
+    void* seh_closure;
+#endif
 };
 
 // Metadata stub for the variable-size cpu context used with uc_context_*()