implement more accurately inaccurate frsqrte

src/xenia/cpu/backend/x64/x64_backend.h

@@ -193,6 +193,7 @@ class X64Backend : public Backend {
   void* reserved_store_64_helper = nullptr;
   void* vrsqrtefp_vector_helper = nullptr;
   void* vrsqrtefp_scalar_helper = nullptr;
+  void* frsqrtefp_helper = nullptr;
  private:
 #if XE_X64_PROFILER_AVAILABLE == 1
   GuestProfilerData profiler_data_;