message: Fix some empty struct build warnings in TFLite
diff: @@ -25,6 +25,11 @@ extern "C" {
  // TODO(aselle): Consider using "if this then that" for testing.
  +// Useful placeholder to put in otherwise empty structs to avoid size warnings.
  +typedef struct {
  + char dummy;
  +} EmptyStructPlaceholder;
  +
  // IMPORTANT: All new members of structs must be added at the end to ensure
  // backwards compatibility.
  @@ -152,9 +157,11 @@ typedef struct {
  } TfLiteAddParams;
  typedef struct {
  + EmptyStructPlaceholder placeholder;
  } TfLiteSpaceToBatchNDParams;
  typedef struct {
  + EmptyStructPlaceholder placeholder;
  } TfLiteBatchToSpaceNDParams;
  typedef struct {
  @@ -230,9 +237,11 @@ typedef struct {
  } TfLiteResizeNearestNeighborParams;
  typedef struct {
  + EmptyStructPlaceholder placeholder;
  } TfLitePadParams;
  typedef struct {
  + EmptyStructPlaceholder placeholder;
  } TfLitePadV2Params;
  typedef struct {
  @@ -272,6 +281,7 @@ typedef struct {
  } TfLiteGatherParams;
  typedef struct {
  + EmptyStructPlaceholder placeholder;
  } TfLiteTransposeParams;
  typedef struct {
  