message: Skip building TF_AcquireFlexDelegate() on Android
  The function is needed to support Flex delegate on Python API.
  Since Android doesn't need it and some NDK tool has a build error on this,
  we'd better skip this on Android.
  This CL fixes issue.
diff: @@ -145,6 +145,7 @@ TfLiteStatus FlexDelegate::CopyFromBufferHandle(
  // Exported C interface function which is used by AcquireFlexDelegate() at
  // interpreter_build.cc. To export the function name globally, the function name
  // must be matched with patterns in tf_version_script.lds
  +#if !defined(__ANDROID__)
  extern "C" {
  #if defined(_WIN32)
  __declspec(dllexport)
  @@ -153,3 +154,4 @@ __declspec(dllexport)
  return tflite::FlexDelegate::Create();
  }
  } // extern "C"
  +#endif // !defined(__ANDROID__)
  